Papers (190) that quote: Pascual-Marqui RD: Standardized low resolution brain electromagnetic tomography (sLORETA): technical details. Methods & Findings in Experimental & Clinical Pharmacology 2002; 24D: 5-12.
Summary: A large percentage of spinal cord-injured subjects suffer from neuropathic pain below the level of the lesion (bNP). The neural mechanisms underlying this condition are not clear. The aim of this study was to elucidate the general effects of spinal deafferentiation and of bNP on electroencephalographic (EEG) activity. In addition, the relationship between the presence of bNP and impaired function of the spinothalamic tract was studied. Measurements were performed in complete and incomplete spinal cord-injured subjects with and without bNP as well as in a healthy control group. Spinothalamic tract function, assessed by contact heat evoked potentials, did not differ between subjects with and without bNP; nevertheless, it was impaired in 94% of subjects suffering from bNP. In the EEG recordings, the degree of deafferentiation was reflected in a slowing of EEG peak frequency in the 6-12-Hz band. Taking into account this unspecific effect, spinal cord-injured subjects with bNP showed significantly slower EEG activity than subjects without bNP. A discrimination analysis in the subjects with spinothalamic tract dysfunction correctly classified 84% of subjects as belonging to either the group with bNP or the group without bNP, according to their EEG peak frequency. These findings could be helpful for both the development of an objective diagnosis of bNP and for testing the effectiveness of new therapeutic agents. © Federation of European Neuroscience Societies and Blackwell Publishing Ltd.
2. Wipf, D. and S. Nagarajan, A unified Bayesian framework for MEG/EEG source imaging. NeuroImage, 2009. 44(3): p. 947-966.
Summary: The ill-posed nature of the MEG (or related EEG) source localization problem requires the incorporation of prior assumptions when choosing an appropriate solution out of an infinite set of candidates. Bayesian approaches are useful in this capacity because they allow these assumptions to be explicitly quantified using postulated prior distributions. However, the means by which these priors are chosen, as well as the estimation and inference procedures that are subsequently adopted to affect localization, have led to a daunting array of algorithms with seemingly very different properties and assumptions. From the vantage point of a simple Gaussian scale mixture model with flexible covariance components, this paper analyzes and extends several broad categories of Bayesian inference directly applicable to source localization including empirical Bayesian approaches, standard MAP estimation, and multiple variational Bayesian (VB) approximations. Theoretical properties related to convergence, global and local minima, and localization bias are analyzed and fast algorithms are derived that improve upon existing methods. This perspective leads to explicit connections between many established algorithms and suggests natural extensions for handling unknown dipole orientations, extended source configurations, correlated sources, temporal smoothness, and computational expediency. Specific imaging methods elucidated under this paradigm include the weighted minimum ℓ2-norm, FOCUSS, minimum current estimation, VESTAL, sLORETA, restricted maximum likelihood, covariance component estimation, beamforming, variational Bayes, the Laplace approximation, and automatic relevance determination, as well as many others. Perhaps surprisingly, all of these methods can be formulated as particular cases of covariance component estimation using different concave regularization terms and optimization rules, making general theoretical analyses and algorithmic extensions/improvements particularly relevant. © 2008.
3. Van Strien, J.W., S.J.E. Langeslag, N.J. Strekalova, L. Gootjes, and I.H.A. Franken, Valence interacts with the early ERP old/new effect and arousal with the sustained ERP old/new effect for affective pictures. Brain Research, 2009. 1251(C): p. 223-235.
Summary: To examine whether valence and arousal influence recognition memory during early automatic or during more sustained processes, event-related brain potentials (ERPs) of 21 women were recorded while they made old/new judgments in a continuous recognition task with pictures from the International Affective Picture System. The pictures were presented twice and differed in emotional valence and arousal. The P1 peak and four time windows were investigated: 200-300 ms, 300-400 ms, 400-600 ms, and 750-1000 ms after stimulus onset. There was a robust old/new effect starting in the 200-300 ms epoch and lasting all time windows. The valence effect was mainly present in the P1 peak and the 200-400 ms epoch, whereas the arousal effect was found in the 300-1000 ms epoch. Exploratory sLORETA analyses dissociated valence-dependent ventromedial prefrontal activity and arousal-dependent occipital activity in the 350-380 ms time window. Valence interacted with the 200-400 ms old/new effect at central and frontal sites. Arousal interacted with the 750-1000 ms old/new effect at posterior sites. It is concluded that valence influences fast recognition memory, while arousal may influence sustained encoding. © 2008 Elsevier B.V. All rights reserved.
4. Valdés-Sosa, P.A., M. Vega-Hernández, J.M. Sánchez-Bornot, E. Martínez-Montes, and M.A. Bobes, EEG source imaging with spatio-temporal tomographic nonnegative independent component analysis. Human Brain Mapping, 2009. 30(6): p. 1898-1910.
Summary: This article describes a spatio-temporal EEG/MEG source imaging (ESI) that extracts a parsimonious set of "atoms" or components, each the outer product of both a spatial and a temporal signature. The sources estimated are localized as smooth, minimally overlapping patches of cortical activation that are obtained by constraining spatial signatures to be nonnegative (NN), orthogonal, sparse, and smooth-in effect integrating ESI with NN-ICA. This constitutes a generalization of work by this group on the use of multiple penalties for ESI. A multiplicative update algorithm is derived being stable, fast and converging within seconds near the optimal solution. This procedure, spatio-temporal tomographic NN ICA (STTONNICA), is equally able to recover superficial or deep sources without additional weighting constraints as tested with simulations. STTONNICA analysis of ERPs to familiar and unfamiliar faces yields an occipital-fusiform atom activated by all faces and a more frontal atom that only is active with familiar faces. The temporal signatures are at present unconstrained but can be required to be smooth, complex, or following a multivariate autoregressive model. © 2009 Wiley-Liss, Inc.
5. Utama, N.P., A. Takemoto, Y. Koike, and K. Nakamura, Phased processing of facial emotion: An ERP study. Neuroscience Research, 2009. 64(1): p. 30-40.
Summary: We examined the temporal characteristics of facial-emotion processing. The stimuli were several morphed images containing seven facial emotions (neutral, anger, happiness, disgust, sadness, surprise, and fear) and ten-graded intensity levels to parametrically control these aspects of facial emotions. Brain activity was recorded with electroencephalography as the subjects detected the facial emotion and assessed its intensity. We found that the temporal profile of detection was quite different from the assessment of intensity. A positive component 100 ms after stimulus onset (P100) was significantly correlated with the correct detection of facial emotion, whereas a negative component 170 ms after stimulus onset (N170) was significantly correlated with the assessment of intensity level. The source of both the P100 and N170 signals was consistently localized to the right occipito-parietal region. We propose phased processing of facial emotion, in which rapid detection of any facial emotion occurs within 100 ms and detailed processing, including the assessment of the intensity, occurs shortly afterwards. © 2009 Elsevier Ireland Ltd and the Japan Neuroscience Society.
6. Tombini, M., F. Zappasodi, L. Zollo, G. Pellegrino, G. Cavallo, F. Tecchio, E. Guglielmelli, and P.M. Rossini, Brain activity preceding a 2D manual catching task. NeuroImage, 2009. 47(4): p. 1735-1746.
Summary: We investigated the event-related desynchronization (ERD) and synchronization (ERS) properties of cortical EEG rhythms in regions of interest (ROI) during the preparation of a 2D task for manual catching of a moving object. EEG signals were recorded through a 32-channel system in eleven healthy subjects during the interception task consisting of 2D catching with the right hand of a handle moving at constant velocity (1.5 m/s) on a predefined straight trajectory. The first session of catching movements (CATCHING_PRE) was compared with a second session after 1 h with identical characteristics (CATCHING_POST) and with other two conditions, where the subjects had to reach and grasp the handle fixed in the medium of platform (REACHING) and they looked at the object moving without catching it (GAZE TRACKING). Changes of cortical rhythms were correlated with dynamic and kinematic indexes of motor performance in both catching sessions. Movements requiring different strategies (predictive versus prospective) are supported by specific changes of cortical EEG rhythms: in the CATCHING condition a more evident power decrease (ERD) in alpha 2 and beta band in the sensorimotor region contralateral to the catching hand was observed, while in the REACHING one a bilateral ERD in beta band was found. Motor learning and movement automatization were characterized by a significant reduction of theta ERS in the anterior cingulate cortex (ACC), a ROI linked to focused attention, and with a shift of neuronal activation in alpha 2 band from the bilateral superior parietal areas to the homologous area of the left hemisphere. Finally, our EEG findings are consistent with the role of supplementary motor (SMA), premotor and prefrontal areas in motor planning and preparation. In particular, theta ERS in left SMA significantly correlated with an improvement of motor performance, as evidenced by its correlation with the training-related reduction of interception time (IT). © 2009 Elsevier Inc. All rights reserved.
7. Tamaki, M., T. Matsuoka, H. Nittono, and T. Hori, Activation of fast sleep spindles at the premotor cortex and parietal areas contributes to motor learning: A study using sLORETA. Clinical Neurophysiology, 2009. 120(5): p. 878-886.
Summary: Objective: The present study examined whether slow and/or fast sleep spindles are related to visuomotor learning, by examining the densities of current sleep spindle activities. Methods: Participants completed a visuomotor task before and after sleep on the learning night. This task was not performed on the non-learning night. Standard polysomnographic recordings were made. After the amplitudes of slow and fast spindles were calculated, sLORETA was used to localize the source of slow and fast spindles and to investigate the relationship between spindle activity and motor learning. Results: Fast spindle amplitude was significantly larger on the learning than on the non-learning nights, particularly at the left frontal area. sLORETA revealed that fast spindle activities in the left frontal and left parietal areas were enhanced when a new visuomotor skill was learned. There were no significant learning-dependent changes in slow spindle activity. Conclusions: Fast spindle activity increases in cortical areas that are involved in learning a new visuomotor skill. The thalamocortical network that underlies the generation of fast spindles may contribute to the synaptic plasticity that occurs during sleep. Significance: Activity of fast sleep spindles is a possible biomarker of memory deficits. © 2009 International Federation of Clinical Neurophysiology.
8. Sumiyoshi, T., Y. Higuchi, T. Itoh, M. Matsui, H. Arai, M. Suzuki, M. Kurachi, C. Sumiyoshi, and Y. Kawasaki, Effect of perospirone on P300 electrophysiological activity and social cognition in schizophrenia: A three-dimensional analysis with sLORETA. Psychiatry Research - Neuroimaging, 2009. 172(3): p. 180-183.
Summary: The purpose of this study was to determine if perospirone, a second generation antipsychotic drug and partial agonist at serotonin-5-HT1A receptors, enhances electrophysiological activity, such as event-related potentials (ERPs), in frontal brain regions, as well as cognitive function in subjects with schizophrenia. P300 current source images were obtained by means of standardized low resolution brain electromagnetic tomography (sLORETA) before and after treatment with perospirone for 6 months. Perospirone significantly increased P300 current source density in the left superior frontal gyrus, and improved positive symptoms and performance on the script tasks, a measure of verbal social cognition, while verbal learning memory tended to be improved. There was a significant correlation between the changes in P300 amplitude on the left frontal lead and those in social cognition. These results suggest the changes in three-dimensional distribution of cortical activity, as demonstrated by sLORETA, may mediate some of the actions of antipsychotic drugs. The distinct cognition-enhancing profile of perospirone in patients with schizophrenia may be related to its actions on 5-HT1A receptors. © 2008 Elsevier Ireland Ltd. All rights reserved.
9. Schumacher, R., M. Wirth, W.J. Perrig, W. Strik, and T. Koenig, ERP correlates of superordinate category activation. International Journal of Psychophysiology, 2009. 72(2): p. 134-144.
Summary: The human semantic network is hierarchically organized, containing superordinate, basic and subordinate levels. Various impairments are thought to be connected with abnormal access to superordinate concepts. We devised an ERP paradigm to examine the activation of superordinate versus otherwise related concepts in 20 healthy participants. Following the presentation of a typical category member an arrow indicated whether the appropriate superordinate category had to be generated (categorization task) or an otherwise related word (relation task). To control task execution, a second word was presented for which a match-mismatch-judgment was required. Reaction times, accuracy rates and ERPs after the second word showed that participants successfully accessed the superordinate category name and that verification in the categorization task was faster and easier than in the relation task. Comparison of ERPs after the arrow revealed topographical, Global Field Power (GFP), and onset latency differences between the two tasks and thus indicated the involvement of at least partially different neural generators. Source localization analysis confirmed that brain regions were activated that were also identified in previous experiments with semantic task. The paradigm seems to be suitable for further examination of superordinate activation processes and evaluation of impairments such as thought disorders in schizophrenic patients. © 2008 Elsevier B.V. All rights reserved.
10. Schneider, S. and H.K. Strüder, Monitoring effects of acute hypoxia on brain cortical activity by using electromagnetic tomography. Behavioural Brain Research, 2009. 197(2): p. 476-480.
Summary: The influences of inadequate brain oxygen supply on cognitive and sensorimotor performance are well documented. However, hemodynamic neuroimaging of brain processes under hypoxic conditions has been limited by the organisational constraints of the methodological framework. This study proposes that standardised low-resolution brain electromagnetic tomography (sLORETA) is a suitable and feasible tool for localising brain cortical processes under hypoxic conditions. Electroencephalograms (EEG) from 21 subjects were recorded prior to, and following 40 min of, exposure to normoxic (21 kPa PIO2) or hypoxic (12.7 kPa PIO2) conditions, Changes in brain cortical activity were localised using sLORETA. Subjects showed an increase in beta-1 activity following hypoxic exposure. This increase in activity was localised in the right superior frontal gyrus (Brodmann area 10). The results are discussed in terms of the relationship between the activation of prefrontal areas under hypoxic conditions and performance deficits. Furthermore, the study demonstrates that sLORETA can be a valuable and reliable alternative for brain imaging when hemodynamic approaches, such as PET or fMRI, are not feasible. © 2008 Elsevier B.V. All rights reserved.
11. Schneider, S., S. Guardiera, T. Abel, H. Carnahan, and H.K. Strüder, Artificial gravity results in changes in frontal lobe activity measured by EEG tomography. Brain Research, 2009. 1285: p. 119-126.
Summary: Mental and perceptual motor performance has been reported to be impaired during hypergravity. Current research has focused on physiological explanations (e.g., deficient proprioceptive feedback) and neglected psycho-physiological effects (e.g., arousal, emotion, cognitive engagement). This study aims at localising changes in brain cortical activity by using a distributed source localisation algorithm (sLORETA) to model the probable neural generators of changes in scalp voltage under hypergravity conditions. Brain cortical activity was measured by EEG before, during and after exposure to three time terrestrial gravity (3Gz) on ten naive subjects aged 29 ± 5 years. Changes in EEG activity were localised using standardised low resolution brain electromagnetic tomography (sLORETA) for alpha-1 [7.5-10 Hz], alpha-2 [10-12.5 Hz], beta-1 [12.5-18 Hz], beta-2 [18-35 Hz] and gamma [35-45 Hz] activities. Individual concentrations of blood cortisol and perceived psychological strain were related to changes in cortical current density. An increase in alpha-1 activity occurred in the right inferior frontal lobe, beta-1 activity was found to be increased in the limbic lobe during 3Gz. Post acceleration alpha-2 and beta-1 activities declined in frontal, temporal and limbic lobes. Changes in blood cortisol concentrations and perceived strain showed a clear relationship to changes in right sided frontal alpha-1 activity. We conclude that frontal activity during hypergravity may serve as a marker of anxiety. This puts a new light on the debate as to whether cognitive and sensorimotor impairments are attributable to primary physiological effects or secondary psychological effects of a hypergravity environment. © 2009 Elsevier B.V.
12. Schneider, S., V. Brümmer, T. Abel, C.D. Askew, and H.K. Strüder, Changes in brain cortical activity measured by EEG are related to individual exercise preferences. Physiology and Behavior, 2009. 98(4): p. 447-452.
Summary: Exercise is well known to result in changes of brain cortical activity measured by EEG. The aim of this study was (1) to localise exercise induced changes in brain cortical activity using a distributed source localisation algorithm and (2) to show that the effects of exercise are linked to participants' physical exercise preferences. Electrocortical activity (5 min) and metabolical parameters (heart rate, lactate, peak oxygen uptake) of eleven recreational runners were recorded before and after incremental treadmill, arm crank and bicycle ergometry. Electroencephalographic activity was localised using standardised low resolution brain electromagnetic tomography (sLORETA). Results revealed an increase in frontal α activity immediately post exercise whereas increases after bike exercise were found to be localised in parietal regions. All three kinds of exercise resulted in an increase of β activity in Brodmann area 7. Fifteen and thirty minutes post exercise a specific activation pattern (decrease in frontal brain activity-increase in occipital regions) was noticeable for treadmill and bike but not arm crank exercise. We conclude that specific brain activation patterns are linked to different kinds of exercise and participants' physical exercise preferences. © 2009 Elsevier Inc.
13. Schienle, A. and A. Schäfer, In search of specificity: Functional MRI in the study of emotional experience. International Journal of Psychophysiology, 2009. 73(1): p. 22-26.
Summary: The growing availability of functional magnetic resonance imaging (fMRI) with its property of high spatial resolution has energized the search for specific neural substrates of basic emotions and their feeling components. In the present article, we address the question as to whether recent fMRI studies on primary affective experiences have truly helped to pinpoint emotion-specific areas in the human brain or whether these studies are afflicted with methodological problems which make such inferences difficult. As one approach for improvement, we suggest the combination of fMRI with methods characterized by high temporal resolution, such as electroencephalography (EEG). Simultaneous recoding allows the correlation of temporally specific EEG components (e.g., the late positive potential) with regional blood-oxygen-level-dependent (BOLD) signals during affective experiences. Combined information on the source as well as the exact temporal pattern of a neural affective response will help to improve our understanding of emotion-specific brain activation. © 2009 Elsevier B.V. All rights reserved.
14. Schendan, H.E. and S.M. Maher, Object knowledge during entry-level categorization is activated and modified by implicit memory after 200 ms. NeuroImage, 2009. 44(4): p. 1423-1438.
Summary: The timing of activating memory about visual objects is important for theories of human cognition but largely unknown, especially for tasks like entry level categorization that activate semantic memory. We tested an implicit memory-categorization "equivalence" hypothesis of multiple memory systems theory that a cortical system that stores structural knowledge to support entry level categorization also stores long-term, perceptual implicit memory, resulting in priming of this knowledge. Event-related brain potentials (ERPs) were recorded to impoverished pictures of new and repeated objects that were similar in perceptual properties but differed in categorization success. The cortical dynamics of object knowledge were defined using categorization ratings and naming. As predicted, rating, naming, and repetition effects on a frontocentral N350 show that implicit memory modifies the object knowledge network supporting categorization. This ERP is a complex of components between 200 and 500 ms indexing temporally overlapping substates from more perceptual to more conceptual knowledge. A frontopolar N350 subcomponent defines the first substate of a process of object model selection from occipitotemporal cortex based on shape similarity, and indicates that implicit memory in this system is greater with better categorization success. Afterwards, parietal positivity and a slow wave index secondary, post-model selection processes, like evaluating the success of a decision or memory match, and working memory for overt report, respectively. Altogether, ERP findings support the equivalence hypothesis and a two-state interactive account of visual object knowledge, and delineate the timing of multiple memory systems. © 2008 Elsevier Inc. All rights reserved.
15. Sauseng, P., W. Klimesch, C. Gerloff, and F.C. Hummel, Spontaneous locally restricted EEG alpha activity determines cortical excitability in the motor cortex. Neuropsychologia, 2009. 47(1): p. 284-288.
Summary: There is growing interest in the functional meaning of rhythmical brain activity. For oscillatory brain activity around 10 Hz in the human electroencephalogram (EEG) it is discussed whether it is associated with the level of cortical excitation. However, it is not clear whether the relation between 10 Hz EEG oscillatory activity and cortical excitability is a global, locally very unspecific phenomenon or whether focal 10 Hz oscillations in the human brain are a highly specific correlate of the cortical excitation level. To determine this open question, multichannel EEG was combined with transcranial magnetic stimulation (TMS) applied to the primary motor cortex in this study. The present data showed that a motor evoked potential was elicited more easily when alpha power immediately preceding the magnetic pulse was low, and vice versa. Interestingly, this effect was only found for very local EEG alpha activity at sites overlying the cortical motor areas to which the TMS pulses were applied. This was verified using source localization in 3D space. These data provide evidence that the magnitude of motor cortical excitability is determined by the amount of topographically specific alpha oscillations in the sensorimotor cortex. © 2008 Elsevier Ltd. All rights reserved.
16. Sabbagh, M.A., L.C. Bowman, L.E. Evraire, and J.M.B. Ito, Neurodevelopmental correlates of theory of mind in preschool children. Child Development, 2009. 80(4): p. 1147-1162.
Summary: Baseline electroencephalogram (EEG) data were collected from twenty-nine 4-year-old children who also completed batteries of representational theory-of-mind (RTM) tasks and executive functioning (EF) tasks. Neural sources of children's EEG alpha (6-9 Hz) were estimated and analyzed to determine whether individual differences in regional EEG alpha activity predicted children's RTM performance, while statistically controlling for children's age and EF skills. Results showed that individual differences in EEG alpha activity localized to the dorsal medial prefrontal cortex (dMPFC) and the right temporal-parietal juncture (rTPJ) were positively associated with children's RTM performance. These findings suggest that the maturation of dMPFC and rTPJ is a critical constituent of preschoolers' explicit theory-of-mind development. © 2009, Society for Research in Child Development, Inc.
17. Rullmann, M., A. Anwander, M. Dannhauer, S.K. Warfield, F.H. Duffy, and C.H. Wolters, EEG source analysis of epileptiform activity using a 1 mm anisotropic hexahedra finite element head model. NeuroImage, 2009. 44(2): p. 399-410.
Summary: The major goal of the evaluation in presurgical epilepsy diagnosis for medically intractable patients is the precise reconstruction of the epileptogenic foci, preferably with non-invasive methods. This paper evaluates whether surface electroencephalography (EEG) source analysis based on a 1 mm anisotropic finite element (FE) head model can provide additional guidance for presurgical epilepsy diagnosis and whether it is practically feasible in daily routine. A 1 mm hexahedra FE volume conductor model of the patient's head with special focus on accurately modeling the compartments skull, cerebrospinal fluid (CSF) and the anisotropic conducting brain tissues was constructed using non-linearly co-registered T1-, T2- and diffusion-tensor-magnetic resonance imaging data. The electrodes of intra-cranial EEG (iEEG) measurements were extracted from a co-registered computed tomography image. Goal function scan (GFS), minimum norm least squares (MNLS), standardized low resolution electromagnetic tomography (sLORETA) and spatio-temporal current dipole modeling inverse methods were then applied to the peak of the averaged ictal discharges EEG data. MNLS and sLORETA pointed to a single center of activity. Moving and rotating single dipole fits resulted in an explained variance of more than 97%. The non-invasive EEG source analysis methods localized at the border of the lesion and at the border of the iEEG electrodes which mainly received ictal discharges. Source orientation was towards the epileptogenic tissue. For the reconstructed superficial source, brain conductivity anisotropy and the lesion conductivity had only a minor influence, whereas a correct modeling of the highly conducting CSF compartment and the anisotropic skull was found to be important. The proposed FE forward modeling approach strongly simplifies meshing and reduces run-time (37 ms for one forward computation in the model with 3.1 million unknowns), corroborating the practical feasibility of the approach. © 2008 Elsevier Inc.
18. Rosazza, C., Q. Cai, L. Minati, Y. Paulignan, and T.A. Nazir, Early involvement of dorsal and ventral pathways in visual word recognition: An ERP study. Brain Research, 2009. 1272(C): p. 32-44.
Summary: Visual expertise underlying reading is attributed to processes involving the left ventral visual pathway. However, converging evidence suggests that the dorsal visual pathway is also involved in early levels of visual word processing, especially when words are presented in unfamiliar visual formats. In the present study, event-related potentials (ERPs) were used to investigate the time course of the early engagement of the ventral and dorsal pathways during processing of orthographic stimuli (high and low frequency words, pseudowords and consonant strings) by manipulating visual format (familiar horizontal vs. unfamiliar vertical format). While early ERP components (P1 and N1) already distinguished between formats, the effect of stimulus type emerged at the latency of the N2 component (225-275 ms). The N2 scalp topography and sLORETA source localisation for this differentiation showed an occipito-temporal negativity for the horizontal format and a negativity that extended towards the dorsal regions for the vertical format. In a later time window (350-425 ms) ERPs elicited by vertically displayed stimuli distinguished words from pseudowords in the ventral area, as confirmed by source localisation. The sustained contribution of occipito-temporal processes for vertical stimuli suggests that the ventral pathway is essential for lexical access. Parietal regions appear to be involved when a serial mechanism of visual attention is required to shift attention from one letter to another. The two pathways cooperate during visual word recognition and processing in these pathways should not be considered as alternative but as complementary elements of reading. © 2009 Elsevier B.V. All rights reserved.
19. Romero, S., M.A. Mañanas, and M.J. Barbanoj, Influence of ocular filtering in eeg data on the assessment of drug-induced effects on the brain, in Human Brain Mapping. 2009. p. 1470-1480.
20. Riggs, L., S.N. Moses, T. Bardouille, A.T. Herdman, B. Ross, and J.D. Ryan, A complementary analytic approach to examining medial temporal lobe sources using magnetoencephalography. NeuroImage, 2009. 45(2): p. 627-642.
Summary: Neuropsychological and neuroimaging findings reveal that the hippocampus is important for recognition memory. However, it is unclear when and whether the hippocampus contributes differentially to recognition of previously studied items (old) versus novel items (new), or contributes to a general processing requirement that is necessary for recognition of both types of information. To address this issue, we examined the temporal dynamics and spectral frequency underlying hippocampal activity during recognition of old/new complex scenes using magnetoencephalography (MEG). In order to provide converging evidence to existing literature in support of the potential of MEG to localize the hippocampus, we reconstructed brain source activity using the beamformer method and analyzed three types of processing-related signal changes by applying three different analysis methods: (1) Synthetic aperture magnetometry (SAM) revealed event related and non-event-related spectral power changes; (2) Inter-trial coherence (ITC) revealed time-locked changes in neural synchrony; and (3) Event-related SAM (ER-SAM) revealed averaged event-related responses over time. Hippocampal activity was evident for both old and new information within the theta frequency band and during the first 250 ms following stimulus onset. The early onset of hippocampal responses suggests that general comparison processes related to recognition of new/old information may occur obligatorily. © 2008 Elsevier Inc. All rights reserved.
21. Pratt, H., A. Starr, H.J. Michalewski, A. Dimitrijevic, N. Bleich, and N. Mittelman, Auditory-evoked potentials to frequency increase and decrease of high- and low-frequency tones. Clinical Neurophysiology, 2009. 120(2): p. 360-373.
Summary: Objective: To define cortical brain responses to large and small frequency changes (increase and decrease) of high- and low-frequency tones. Methods: Event-Related Potentials (ERPs) were recorded in response to a 10% or a 50% frequency increase from 250 or 4000 Hz tones that were approximately 3 s in duration and presented at 500-ms intervals. Frequency increase was followed after 1 s by a decrease back to base frequency. Frequency changes occurred at least 1 s before or after tone onset or offset, respectively. Subjects were not attending to the stimuli. Latency, amplitude and source current density estimates of ERPs were compared across frequency changes. Results: All frequency changes evoked components P50, N100, and P200. N100 and P200 had double peaks at bilateral and right temporal sites, respectively. These components were followed by a slow negativity (SN). The constituents of N100 were predominantly localized to temporo-parietal auditory areas. The potentials and their intracranial distributions were affected by both base frequency (larger potentials to low frequency) and direction of change (larger potentials to increase than decrease), as well as by change magnitude (larger potentials to larger change). The differences between frequency increase and decrease depended on base frequency (smaller difference to high frequency) and were localized to frontal areas. Conclusions: Brain activity varies according to frequency change direction and magnitude as well as base frequency. Significance: The effects of base frequency and direction of change may reflect brain networks involved in more complex processing such as speech that are differentially sensitive to frequency modulations of high (consonant discrimination) and low (vowels and prosody) frequencies. © 2008 International Federation of Clinical Neurophysiology.
22. Pratt, H., A. Starr, H.J. Michalewski, A. Dimitrijevic, N. Bleich, and N. Mittelman, Cortical evoked potentials to an auditory illusion: Binaural beats. Clinical Neurophysiology, 2009. 120(8): p. 1514-1524.
Summary: Objective: To define brain activity corresponding to an auditory illusion of 3 and 6 Hz binaural beats in 250 Hz or 1000 Hz base frequencies, and compare it to the sound onset response. Methods: Event-Related Potentials (ERPs) were recorded in response to unmodulated tones of 250 or 1000 Hz to one ear and 3 or 6 Hz higher to the other, creating an illusion of amplitude modulations (beats) of 3 Hz and 6 Hz, in base frequencies of 250 Hz and 1000 Hz. Tones were 2000 ms in duration and presented with approximately 1 s intervals. Latency, amplitude and source current density estimates of ERP components to tone onset and subsequent beats-evoked oscillations were determined and compared across beat frequencies with both base frequencies. Results: All stimuli evoked tone-onset P50, N100 and P200 components followed by oscillations corresponding to the beat frequency, and a subsequent tone-offset complex. Beats-evoked oscillations were higher in amplitude with the low base frequency and to the low beat frequency. Sources of the beats-evoked oscillations across all stimulus conditions located mostly to left lateral and inferior temporal lobe areas in all stimulus conditions. Onset-evoked components were not different across stimulus conditions; P50 had significantly different sources than the beats-evoked oscillations; and N100 and P200 sources located to the same temporal lobe regions as beats-evoked oscillations, but were bilateral and also included frontal and parietal contributions. Conclusions: Neural activity with slightly different volley frequencies from left and right ear converges and interacts in the central auditory brainstem pathways to generate beats of neural activity to modulate activities in the left temporal lobe, giving rise to the illusion of binaural beats. Cortical potentials recorded to binaural beats are distinct from onset responses. Significance: Brain activity corresponding to an auditory illusion of low frequency beats can be recorded from the scalp. © 2009 International Federation of Clinical Neurophysiology.
23. Perre, L., C. Pattamadilok, M. Montant, and J.C. Ziegler, Orthographic effects in spoken language: On-line activation or phonological restructuring? Brain Research, 2009. 1275(C): p. 73-80.
Summary: Previous research has shown that literacy (i.e., learning to read and spell) affects spoken language processing. However, there is an on-going debate about the nature of this influence. Some argued that orthography is co-activated on-line whenever we hear a spoken word. Others suggested that orthography is not activated on-line but has changed the nature of the phonological representations. Finally, both effects might occur simultaneously, that is, orthography might be activated on-line in addition to having changed the nature of the phonological representations. Previous studies have not been able to tease apart these hypotheses. The present study started by replicating the finding of an orthographic consistency effect in spoken word recognition using event-related brain potentials (ERPs): words with multiple spellings (i.e., inconsistent words) differed from words with unique spellings (i.e., consistent words) as early as 330 ms after the onset of the target. We then employed standardized low resolution electromagnetic tomography (sLORETA) to determine the possible underlying cortical generators of this effect. The results showed that the orthographic consistency effect was clearly localized in a classic phonological area (left BA40). No evidence was found for activation in the posterior cortical areas coding orthographic information, such as the visual word form area in the left fusiform gyrus (BA37). This finding is consistent with the restructuring hypothesis according to which phonological representations are "contaminated" by orthographic knowledge. © 2009 Elsevier B.V. All rights reserved.
24. Ortigue, S., N. Patel, and F. Bianchi-Demicheli, New electroencephalogram (EEG) neuroimaging methods of analyzing brain activity applicable to the study of human sexual response. Journal of Sexual Medicine, 2009. 6(7): p. 1830-1845.
Summary: Introduction. Electroencephalogram (EEG) combined with brain source localization algorithms is becoming a powerful tool in the neuroimaging study of human cerebral functions. Aim. The present article provides a tutorial on the various EEG methods currently used to study the human brain activity, notably during sexual response. Main Outcome Measures. Review of published literature on standard EEG waveform analyses and most recent electrical neuroimaging techniques (microstate approach and two methods of brain source localization). Methods. Retrospective overview of pertinent literature. Results. Although the standard EEG waveform analyses enable millisecond time-resolution information about the human sexual responses in the brain, less is clear about their related spatial information. Nowadays, the improvement of EEG techniques and statistical approaches allows the visualization of the dynamics of the human sexual response with a higher spatiotemporal resolution. Here, we describe these enhanced techniques and summarize along with an overview of what we have learned from them in terms of chronoarchitecture of sexual response in the human brain. Finally, the speculation on how we may be able to use other enhanced approaches, such as independent component analysis, are also presented. Conclusions. EEG neuroimaging has already been proven as a strong worthwhile research tool. Combining this approach with standard EEG waveform analyses in sexual medicine may provide a better understanding of the neural activity underlying the human sexual response in both healthy and clinical populations. Ortigue S, Patel N, and Bianchi-Demicheli F. New EEG neuroimaging methods of analyzing brain activity applicable to the study of human sexual response. © 2009 International Society for Sexual Medicine.
25. Olbrich, S., C. Mulert, S. Karch, M. Trenner, G. Leicht, O. Pogarell, and U. Hegerl, EEG-vigilance and BOLD effect during simultaneous EEG/fMRI measurement. NeuroImage, 2009. 45(2): p. 319-332.
Summary: Different EEG-vigilance stages from full alertness to sleep onset can be separated during rest. Also fMRI research recently focused on the resting condition and identified several resting state networks. In order to deepen the understanding of different levels of global brain function from relaxed wakefulness to sleep onset the association between EEG-vigilance stages and BOLD signals was analysed. EEG-vigilance stages were attributed to consecutive 3-sec-EEG-segments by an algorithm using topographic and spectral information. Results of the classification were validated by analysing the heart rates during the different brain states. Vigilance stages served as regressors for the analysis of the simultaneously acquired fMRI data. Additionally resting state networks were derived from the fMRI data using independent component analysis (ICA). Also vigilance associated brain activity revealed by EEG-based standardized low resolution tomography (sLORETA) was compared to the results of the fMRI analysis. Results showed increased BOLD signal in the occipital cortex, the anterior cingulate cortex, the frontal cortex, the parietal cortices and the temporal cortices and decreasing BOLD signals in the thalamus and the frontal cortex for declining vigilance stages (A2, A3, B1, B2/B3) in comparison to the high vigilance stage A1. Resting state networks revealed a spatial overlap with the vigilance stage associated BOLD maps in conjunction analyses. sLORETA showed increased neuroelectric alpha activity at the occipital cortex comparable to occipital BOLD signal decreases when comparing stage A with stage B. Different EEG-vigilance stages during rest are associated with pronounced differences of BOLD signals in several brain areas which partly correspond to the resting state networks. For cognitive fMRI-research it therefore seems important to pay attention to vigilance switches in order to separate vigilance associated BOLD signal changes from those specifically related to cognition. © 2008 Elsevier Inc. All rights reserved.
26. Okamoto, H., H. Stracke, R. Draganova, and C. Pantev, Hemispheric asymmetry of auditory evoked fields elicited by spectral versus temporal stimulus change. Cerebral Cortex, 2009. 19(10): p. 2290-2297.
Summary: The investigation of functional hemispheric asymmetries regarding auditory processing in the human brain still remains a challenge. Classical lesion and recent neuroimaging studies indicated that speech is dominantly processed in the left hemisphere, whereas music is dominantly processed in the right. However, recent studies demonstrated that the functional hemispheric asymmetries were not limited to the processing of highly cognitive sound signals like speech and music but rather originated from the basic neural processing of elementary sound features, that is, spectral and temporal acoustic features. Here, in contrast to previous studies, we used carefully composed tones and pulse trains as stimuli, balanced the overall physical sound input between spectral and temporal change conditions, and demonstrated the time course of neural activity evoked by spectral versus temporal sound input change by means of magnetoencephalography (MEG). These original findings support the hypothesis that spectral change is dominantly processed in the right hemisphere, whereas temporal change is dominantly processed in the left.
27. Murphy, M., B.A. Riedner, R. Huber, M. Massimini, F. Ferrarelli, and G. Tononi, Source modeling sleep slow waves. Proceedings of the National Academy of Sciences of the United States of America, 2009. 106(5): p. 1608-1613.
Summary: Slow waves are the most prominent electroencephalographic (EEG) feature of sleep. These waves arise from the synchronization of slow oscillations in the membrane potentials of millions of neurons. Scalp-level studies have indicated that slow waves are not instantaneous events, but rather they travel across the brain. Previous studies of EEG slow waves were limited by the poor spatial resolution of EEGs and by the difficulty of relating scalp potentials to the activity of the underlying cortex. Here we use high-density EEG (hd-EEG) source modeling to show that individual spontaneous slow waves have distinct cortical origins, propagate uniquely across the cortex, and involve unique subsets of cortical structures. However, when the waves are examined en masse, we find that there are diffuse hot spots of slow wave origins centered on the lateral sulci. Furthermore, slow wave propagation along the anterior-posterior axis of the brain is largely mediated by a cingulate highway. As a group, slow waves are associated with large currents in the medial frontal gyrus, the middle frontal gyrus, the inferior frontal gyrus, the anterior cingulate, the precuneus, and the posterior cingulate. These areas overlap with the major connectional backbone of the cortex and with many parts of the default network. © 2009 by The National Academy of Sciences of the USA.
28. Mobascher, A., J. Brinkmeyer, T. Warbrick, F. Musso, H.J. Wittsack, A. Saleh, A. Schnitzler, and G. Winterer, Laser-evoked potential P2 single-trial amplitudes covary with the fMRI BOLD response in the medial pain system and interconnected subcortical structures. NeuroImage, 2009. 45(3): p. 917-926.
Summary: Pain is a complex experience with sensory, emotional and cognitive aspects. The cortical representation of pain - the pain matrix - consists of a network of regions including the primary (S1) and secondary (S2) sensory cortex, insula, and anterior cingulate cortex (ACC). These structures interact with brain regions such as the prefrontal cortex and the amygdalae. Simultaneous EEG/fMRI (electroencephalography/functional magnetic resonance imaging) has recently been introduced as a method to study the spatiotemporal characteristics of cognitive processes with high spatial and high temporal resolution at the same time. The present study was conducted to clarify if single trial EEG-informed BOLD modeling supports the definition of functional compartments within the pain matrix and interconnected regions. Twenty healthy subjects received painful laser stimulation while EEG and the fMRI blood oxygen level dependent (BOLD) signal were recorded simultaneously. While the laser-evoked N2 potential provided no additional information for BOLD modeling, the regressor obtained from the single trial laser-evoked P2 potential explained additional variance in a network of cortical and subcortical structures that largely overlapped with the pain matrix. This modeling strategy yielded pronounced activation in the ACC, right amygdala and thalamus. Our results suggest that laser-evoked potential (LEP) informed fMRI can be used to visualize BOLD activation in the pain matrix with an emphasis on functional compartments (as defined by the temporal dynamics of the LEP) such as the medial pain system. Furthermore, our findings suggest a concerted effort of the ACC and the amygdala in the cognitive-emotional evaluation of pain. © 2009 Elsevier Inc. All rights reserved.
29. Mitsonis, C.I., C. Potagas, I. Zervas, and K. Sfagos, The effects of stressful life events on the course of multiple sclerosis: A review. International Journal of Neuroscience, 2009. 119(3): p. 315-335.
Summary: There is growing body of evidence that support an association between stressful life events and an increased risk for Multiple Sclerosis (MS) exacerbations. However, the nature of this relationship remains unclear, because of the lack of agreement about the definition of stress and/or because of research design problems. This article summarizes the psychological and biological mechanisms by which stress may impact MS progression. Findings indicate a number of factors, including stressor chronicity, frequency, severity and type, depression, anxiety, health locus of control, optimism, perceived social support, and coping strategies. Applied implications are discussed, concentrating on the need for multidisciplinary care interventions that target patients' disease symptoms. Copyright © 2009 Informa Healthcare USA, Inc.
30. Malecki, U., S. Stallforth, D. Heipertz, N. Lavie, and E. Duzel, Neural generators of sustained activity differ for stimulus-encoding and delay maintenance. European Journal of Neuroscience, 2009. 30(5): p. 924-933.
Summary: The ability to maintain information online beyond sensory stimulation is regarded as a key contribution of working memory to goal-directed behaviour. It is widely accepted that sustained neural activity is a key mechanism of stimulus maintenance, but it is unclear to what extent the neural generators of sustained activity change from stimulus-encoding to maintenance. Using event-related potentials in humans, we show that, in a delayed match-to-sample task, slow shifts over parieto-occipital electrode sites had a different topography and polarity during encoding and delay maintenance of images depicting scenes. This clearly demonstrates that neural generators of sustained activity associated with stimulus-encoding and delay maintenance differed, and that the change between these generators occurred time-locked to the onset of the delay period. We also investigated how monetary reward incentives modulated the amplitude and topography of sustained delay activity and the ability to suppress irrelevant distracting information during the delay. Reward incentives improved maintenance performance and this was correlated with an expansion of the parieto-occipital electrode sites that were entrained into sustained delay activity (rather than improved distractor suppression), suggesting that under the influence of reward, the parieto-occipital regions that contributed to delay maintenance expanded in size. © 2009 Federation of European Neuroscience Societies and Blackwell Publishing Ltd.
31. Lotte, F., A. Lécuyer, and B. Arnaldi, FuRIA: An inverse solution based feature extraction algorithm using fuzzy set theory for brain-computer interfaces. IEEE Transactions on Signal Processing, 2009. 57(8): p. 3253-3263.
Summary: This paper presents FuRIA, a trainable feature extraction algorithm for noninvasive brain-computer interfaces (BCI). FuRIA is based on inverse solutions and on the new concepts of fuzzy region of interest (ROI) and fuzzy frequency band. FuRIA can automatically identify the relevant ROI and frequency bands for the discrimination of mental states, even for multiclass BCI. Once identified, the activity in these ROI and frequency bands can be used as features for any classifier. The evaluations of FuRIA showed that the extracted features were interpretable and can lead to high classification accuracies. © 2009 IEEE.
32. Li, L., D. Yao, and G. Yin, Spatio-temporal dynamics of visual selective attention identified by a common spatial pattern decomposition method. Brain Research, 2009. 1282: p. 84-94.
Summary: Three spatio-temporal neurophysiological patterns involved in visual selective attention were identified from the human event-related potentials (ERPs) by a novel common spatial pattern (CSP) decomposition method and the standardized low resolution brain electromagnetic tomography (sLORETA). In the experiment, stimuli were rapidly presented randomly to the right or left visual fields while subjects attended to one visual field at a time (Clark, Hillyard, 1996. Spatial selective attention affects early extrastriate but not striate components of the visual evoked potential. J. Cogn. Neurosci. 8, 387-402). The spatial patterns indicated that visual cortex, prefrontal cortex (PFC), anterior cingulate cortex (ACC) and posterior parietal cortex (PPC) were involved in the control of top-down attention. The temporal waveforms indicated that contralateral PFC and PPC were activated synchronously at about 150 ms after the stimulus onset, with early attention effects only occurring in PFC, and the PPC was activated earlier than that of PFC during 200-260 ms. The results imply that humans adopt different allocation strategies for resources in visual attention and un-attention situations. For attention case, visual cortex consumes the most resources and for non-attention situation, the ACC and PPC consume the most resources. © 2009 Elsevier B.V. All rights reserved.
33. Laufer, I., M. Negishi, and R.T. Constable, Comparator and non-comparator mechanisms of change detection in the context of speech - An ERP study. NeuroImage, 2009. 44(2): p. 546-562.
Summary: Automatic change detection reflects a cognitive memory-based comparison mechanism as well as a sensorial non-comparator mechanism based on differential states of refractoriness. The purpose of this study was to examine whether the comparator mechanism of the mismatch negativity component (MMN) is differentially affected by the lexical status of the deviant. Event-related potential (ERP) data was collected during an "oddball" paradigm designed to elicit the MMN from 15 healthy subjects that were involved in a counting task. Topography pattern analysis and source estimation were utilized to examine the deviance (deviants vs. standards), cognitive (deviants vs. control counterparts) and refractoriness (standards vs. control counterparts) effects elicited by standard-deviant pairs ("deh-day"; "day-deh"; "teh-tay") embedded within "oddball" blocks. Our results showed that when the change was salient regardless of lexical status (i.e., the /e:/ to /eI/ transition) the response tapped the comparator based-mechanism of the MMN which was located in the cuneus/posterior cingulate, reflected sensitivity to the novelty of the auditory object, appeared in the P2 latency range and mainly involved topography modulations. In contrast, when the novelty was low (i.e., the /eI/ to /e:/ transition) an acoustic change complex was elicited which involved strength modulations over the P1/N1 range and implicated the middle temporal gyrus. This result pattern also resembled the one displayed by the non-comparator mechanism. These findings suggest spatially and temporally distinct brain activities of comparator mechanisms of change detection in the context of speech. © 2008 Elsevier Inc. All rights reserved.
34. Korzyukov, O., E. Asano, V. Gumenyuk, C. Juhász, M. Wagner, R.D. Rothermel, and H.T. Chugani, Intracranial recording and source localization of auditory brain responses elicited at the 50 ms latency in three children aged from 3 to 16 years. Brain Topography, 2009. 22(3): p. 166-175.
Summary: Maturational studies of the auditory-evoked brain response at the 50 ms latency provide an insight into why this response is aberrant in a number of psychiatric disorders that have developmental origin. Here, using intracranial recordings we found that neuronal activity of the primary contributors to this response can be localised at the lateral part of Heschl's gyrus already at the age of 3.5 years. This study provides results to support the notion that deviations in cognitive function(s) attributed to the auditory P50 in adults might involve abnormalities in neuronal activity of the frontal lobe or in the interaction between the frontal and temporal lobes. Validation and localisation of progenitors of the adults' P50 in young children is a much-needed step in the understanding of the biological significance of different subcomponents that comprise the auditory P50 in the adult brain. In combination with other approaches investigating neuronal mechanisms of auditory P50, the present results contribute to the greater understanding of what and why neuronal activity underlying this response is aberrant in a number of brain dysfunctions. Moreover, the present source localisation results of auditory response at the 50 ms latency might be useful in paediatric neurosurgery practice. © 2009 Springer Science+Business Media, LLC.
35. Karakaş, H.M., S. Karakaş, A. Özkan Ceylan, and E.T. Tali, Recording event-related activity under hostile magnetic resonance environment: Is multimodal EEG/ERP-MRI recording possible? International Journal of Psychophysiology, 2009. 73(2): p. 123-132.
Summary: Event-related potentials (ERPs) have high temporal resolution, but insufficient spatial resolution; the converse is true for the functional imaging techniques. The purpose of the study was to test the utility of a multimodal EEG/ERP-MRI technique which combines electroencephalography (EEG) and magnetic resonance imaging (MRI) for a simultaneously high temporal and spatial resolution. The sample consisted of 32 healthy young adults of both sexes. Auditory stimuli were delivered according to the active and passive oddball paradigms in the MRI environment (MRI-e) and in the standard conditions of the electrophysiology laboratory environment (Lab-e). Tasks were presented in a fixed order. Participants were exposed to the recording environments in a counterbalanced order. EEG data were preprocessed for MRI-related artifacts. Source localization was made using a current density reconstruction technique. The ERP waveforms for the MRI-e were morphologically similar to those for the Lab-e. The effect of the recording environment, experimental paradigm and electrode location were analyzed using a 2 × 2 × 3 analysis of variance for repeated measures. The ERP components in the two environments showed parametric variations and characteristic topographical distributions. The calculated sources were in line with the related literature. The findings indicated effortful cognitive processing in MRI-e. The study provided preliminary data on the feasibility of the multimodal EEG/ERP-MRI technique. It also indicated lines of research that are to be pursued for a decisive testing of this technique and its implementation to clinical practice. © 2009 Elsevier B.V. All rights reserved.
36. Jardri, R., D. Pins, M. Bubrovszky, B. Lucas, V. Lethuc, C. Delmaire, V. Vantyghem, P. Despretz, and P. Thomas, Neural functional organization of hallucinations in schizophrenia: Multisensory dissolution of pathological emergence in consciousness. Consciousness and Cognition, 2009. 18(2): p. 449-457.
Summary: Although complex hallucinations are extremely vivid, painful symptoms in schizophrenia, little is known about the underlying mechanisms of multisensory integration in such a phenomenon. We investigated the neural basis of these altered states of consciousness in a patient with schizophrenia, by combining state of the art neuroscientific exploratory methods like functional MRI, diffusion tensor imaging, cortical thickness analysis, electrical source reconstruction and trans-cranial magnetic stimulation. The results shed light on the functional architecture of the hallucinatory processes, in which unimodal information from different modalities is strongly functionally connected to higher-order integrative areas. © 2008 Elsevier Inc. All rights reserved.
37. Him, Y.Y., A.Y. Roh, Y. Namgoong, H.J. Jo, J.M. Lee, and J.S. Kwon, Cortical network dynamics during source memory retrieval: Current density imaging with individual MRI. Human Brain Mapping, 2009. 30(1): p. 78-91.
Summary: We investigated the neural correlates of source memory retrieval using low-resolution electromagnetic tomography (LORETA) with 64 channels EEG and individual MRI as a realistic head model. Event-related potentials (ERPs) were recorded while 13 healthy subjects performed the source memory task for the voice of the speaker in spoken words. The source correct condition of old words elicited more positive-going potentials than the correct rejection condition of new words at 400-700 ms post-stimulus and the old/new effects also appeared in the right anterior region between 1,000 and 1,200 ms. We conducted source reconstruction at mean latencies of 311, 604, 793, and 1,100 ms and used statistical parametric mapping for the statistical analysis. The results of source analysis suggest that the activation of the right inferior parietal region may reflect retrieval of source information. The source elicited by the difference ERPs between the source correct and source incorrect conditions exhibited dynamic change of current density activation in the overall cortices with time during source memory retrieval. These results indicate that multiple neural systems may underlie the ability to recollect context. Hum Brain Mapp 30:78-91, 2009. © 2007 Wiley-Liss, inc.
38. Herrmann, B., B. Maess, A.S. Hasting, and A.D. Friederici, Localization of the syntactic mismatch negativity in the temporal cortex: An MEG study. NeuroImage, 2009. 48(3): p. 590-600.
Summary: Recent auditory oddball studies using syntactic stimuli report a syntactic effect on the mismatch negativity (sMMN) around 100-200 ms. For morphosyntactic violations, this sMMN effect has been localized in the left superior temporal cortex. Independently, a recent visual sentence processing study introduced a "sensory hypothesis" which postulates that sensory cortices are sensitive to syntactic violations when these are overtly marked by closed-class morphemes, and thus contribute to early syntax-related effects in EEG and MEG. The present study aimed to test the sensory hypothesis in the auditory modality by localizing the neuronal sources of the sMMN to phrase structure violations. Using whole head magnetoencephalography, two-word utterances which were syntactically correct, uncommon or incorrect due to a word category violation were presented in an auditory oddball paradigm. In the sMMN time window (100-180 ms), incorrect phrases elicited strongest activation in the left Sylvian fissure (including the primary auditory cortex) and in the left superior temporal sulcus. Prior to this, a very early grammaticality effect (40-80 ms), focused in the left Sylvian fissure, was found. An additional grammaticality effect in a later time window (280-380 ms) was localized in the anterior part of the superior temporal gyrus, the planum polare. Processing of an uncommon phrase did not differ from processing a correct phrase in any of the time windows, indicating the genuinely syntactic nature of the sMMN effect. Our results are in line with previous studies localizing the sMMN to morphosyntactic violations and are furthermore compatible with the sensory hypothesis of closed-class morphology based syntactic processes. © 2009 Elsevier Inc. All rights reserved.
39. Grossheinrich, N., A. Rau, O. Pogarell, K. Hennig-Fast, M. Reinl, S. Karch, A. Dieler, G. Leicht, C. Mulert, A. Sterr, and F. Padberg, Theta Burst Stimulation of the Prefrontal Cortex: Safety and Impact on Cognition, Mood, and Resting Electroencephalogram. Biological Psychiatry, 2009. 65(9): p. 778-784.
Summary: Background: Because standard repetitive transcranial magnetic stimulation (rTMS) protocols exhibit post-stimulus effects of short duration, novel protocols such as theta burst stimulation (TBS), are promising approaches to enhance the effectiveness of rTMS. However, little is known about the side effect profile of such protocols. Thus, the present study explores whether TBS is safe particularly in terms of effects on cognition, mood, and electroencephalogram (EEG) measures in healthy subjects. Methods: Twenty-four healthy volunteers participated in 2 randomized, placebo-controlled, cross-over experiments and underwent continuous TBS (cTBS), intermittent TBS (iTBS), and shamTBS either over the left dorsolateral prefrontal cortex (DLPFC, n = 12) or the medial prefrontal cortices (mPFC, n = 12). Clinical side effects, performance in a neuropsychological battery, mood changes, and resting EEG were recorded. Results: Neither a seizure nor epileptiform EEG activity was observed. The most prominent side effect was the occurrence of vagal reactions during TBS; otherwise no serious side effects were found. Standardized low-resolution brain electromagnetic tomography showed current density changes in the α2 band after iTBS of the DLPFC, which remained detectable up to 50 min after stimulation. The few changes in neuropsychological performance were concordant with stimulation site. No impact on mood was detected. Conclusions: Although TBS protocols of the human prefrontal cortex seem to be safe in healthy subjects, future studies need to address the occurrence of vagal reactions. Excitatory and inhibitory properties of motor cortex TBS might not be transferable to prefrontal sites, and the action of specific TBS protocols needs to be further investigated prior to clinical application. © 2009 Society of Biological Psychiatry.
40. Gianotti, L.R.R., D. Knoch, P.L. Faber, D. Lehmann, R.D. Pascual-Marqui, C. Diezi, C. Schoch, C. Eisenegger, and E. Fehr, Tonic activity level in the right prefrontal cortex predicts individuals' risk taking. Psychological Science, 2009. 20(1): p. 33-38.
Summary: Human risk taking is characterized by a large amount of individual heterogeneity. In this study, we applied resting-state electroencephalography, which captures stable individual differences in neural activity, before subjects performed a risk-taking task. Using a source-localization technique, we found that the baseline cortical activity in the right prefrontal cortex predicts individual risk-taking behavior. Individuals with higher baseline cortical activity in this brain area display more risk aversion than do other individuals. This finding demonstrates that neural characteristics that are stable over time can predict a highly complex behavior such as risk-taking behavior and furthermore suggests that hypoactivity in the right prefrontal cortex might serve as a dispositional indicator of lower regulatory abilities, which is expressed in greater risk-taking behavior. © 2009 Association for Psychological Science.
41. Frühholz, S., T. Fehr, and M. Herrmann, Early and late temporo-spatial effects of contextual interference during perception of facial affect. International Journal of Psychophysiology, 2009. 74(1): p. 1-13.
Summary: Contextual features during recognition of facial affect are assumed to modulate the temporal course of emotional face processing. Here, we simultaneously presented colored backgrounds during valence categorizations of facial expressions. Subjects incidentally learned to perceive negative, neutral and positive expressions within a specific colored context. Subsequently, subjects made fast valence judgments while presented with the same face-color-combinations as in the first run (congruent trials) or with different face-color-combinations (incongruent trials). Incongruent trials induced significantly increased response latencies and significantly decreased performance accuracy. Contextual incongruent information during processing of neutral expressions modulated the P1 and the early posterior negativity (EPN) both localized in occipito-temporal areas. Contextual congruent information during emotional face perception revealed an emotion-related modulation of the P1 for positive expressions and of the N170 and the EPN for negative expressions. Highest amplitude of the N170 was found for negative expressions in a negatively associated context and the N170 amplitude varied with the amount of overall negative information. Incongruent trials with negative expressions elicited a parietal negativity which was localized to superior parietal cortex and which most likely represents a posterior manifestation of the N450 as an indicator of conflict processing. A sustained activation of the late LPP over parietal cortex for all incongruent trials might reflect enhanced engagement with facial expression during task conditions of contextual interference. In conclusion, whereas early components seem to be sensitive to the emotional valence of facial expression in specific contexts, late components seem to subserve interference resolution during emotional face processing. © 2009 Elsevier B.V. All rights reserved.
42. Franken, I.H.A., L. Gootjes, and J.W. Van Strien, Automatic processing of emotional words during an emotional Stroop task. NeuroReport, 2009. 20(8): p. 776-781.
Summary: There is evidence that early event-related potential components, such as the early posterior negativity (EPN; 200-300 ms), are modulated by emotional words. This study addressed the automaticity of this early response in an emotional Stroop task. The results show that the EPN was modulated by emotional connotation. In addition, an enhanced frontal P3 and an enhanced, more broadly distributed, late positive potential emerged as response to emotional words. The present results suggest that this early event-related potential activity represents the fast and automatic processing of emotional words. Furthermore, as the EPN originates from the posterior visual association cortex, the present results suggest a role of these areas in the automatic processing of emotional connotation. © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins.
43. Esposito, F., C. Mulert, and R. Goebel, Combined distributed source and single-trial EEG-fMRI modeling: Application to effortful decision making processes. NeuroImage, 2009. 47(1): p. 112-121.
Summary: Single-trial coupling of simultaneously recorded EEG and fMRI time-series can be used to generate fMRI patterns of brain activity with high spatial resolution from EEG responses with high temporal resolution. A forced choice reaction task under different effort conditions has been previously used to demonstrate single-trial EEG-fMRI coupling effects for an early ERP component (N1: 70-150 ms) measured on a single scalp channel (Cz), thereby providing the first multi-modal evidence of early anterior cingulate cortex (ACC) activation in effortful decision making (Mulert, C., Seifert, C., Leicht, G., Kirsch, V., Ertl, M., Karch, S., Moosmann, M., Lutz, J., Möller, H.J., Hegerl, U., Pogarell, O., Jäger, L., 2008. Single-trial coupling of EEG and fMRI reveals the involvement of early anterior cingulate cortex activation in effortful decision making. Neuroimage 42, 158-168.). In this work, we searched for "effort-specific" ERP-N1 sources and explored their single-trial EEG-fMRI correlations for discovering "source-specific" inter-modality coupling effects. To this end, we performed a whole-cortex distributed ERP analysis and used the local source power trial-by-trial variation as an input for single-trial EEG-fMRI coupling analysis. We found a high-effort-specific ERP-N1 source in the ACC and statistically significant differential EEG-fMRI coupling spots in five cortical regions, including the ACC. Our results provide new insights about the neural origins of effort-specific EEG and fMRI response modulations in a choice reaction task and confirm the central role of early ACC activation in motivation-related decision making processes; we discuss the importance of combining distributed source modeling with single-trial coupling for enriching the interpretation of EEG-fMRI patterns. © 2009 Elsevier Inc. All rights reserved.
44. Esposito, F., A. Aragri, T. Piccoli, G. Tedeschi, R. Goebel, and F. Di Salle, Distributed analysis of simultaneous EEG-fMRI time-series: modeling and interpretation issues. Magnetic Resonance Imaging, 2009. 27(8): p. 1120-1130.
Summary: Functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) represent brain activity in terms of a reliable anatomical localization and a detailed temporal evolution of neural signals. Simultaneous EEG-fMRI recordings offer the possibility to greatly enrich the significance and the interpretation of the single modality results because the same neural processes are observed from the same brain at the same time. Nonetheless, the different physical nature of the measured signals by the two techniques renders the coupling not always straightforward, especially in cognitive experiments where spatially localized and distributed effects coexist and evolve temporally at different temporal scales. The purpose of this article is to illustrate the combination of simultaneously recorded EEG and fMRI signals exploiting the principles of EEG distributed source modeling. We define a common source space for fMRI and EEG signal projection and gather a conceptually unique framework for the spatial and temporal comparative analysis. We illustrate this framework in a graded-load working-memory simultaneous EEG-fMRI experiment based on the n-back task where sustained load-dependent changes in the blood-oxygenation-level-dependent (BOLD) signals during continuous item memorization co-occur with parametric changes in the EEG theta power induced at each single item. In line with previous studies, we demonstrate on two single-subject cases how the presented approach is capable of colocalizing in midline frontal regions two phenomena simultaneously observed at different temporal scales, such as the sustained negative changes in BOLD activity and the parametric EEG theta synchronization. We discuss the presented approach in relation to modeling and interpretation issues typically arising in simultaneous EEG-fMRI studies. © 2009 Elsevier Inc. All rights reserved.
45. Dümpelmann, M., J. Fell, J. Wellmer, H. Urbach, and C.E. Elger, 3D source localization derived from subdural strip and grid electrodes: A simulation study. Clinical Neurophysiology, 2009. 120(6): p. 1061-1069.
Summary: Objective: Little experience exists in the application of source reconstruction methods to recordings from subdural strip and grid electrodes. This study addressed the question, whether reliable and accurate 3D source localization is possible from the Electrocorticogram (ECoG). Methods: The accuracy of source reconstruction was investigated by simulations and a case study. Simulated sources were used to compute potentials at the electrode positions derived from the MRI of a patient with subdural electrodes. Used procedures were the linear estimation (minimum norm) algorithm and the MUSIC (MUltiple SIgnal Classification) scan. Results: Maxima of linear estimation were attracted to adjacent electrodes. Reliable localization with a localization error ≤15 mm was only achieved for about 35% of the original source positions. Maxima of the MUSIC metric were identical to original positions for simulations without noise. Noise reduced the percentage of reliable solutions down to a 79.0%. Electrode contacts distant to the source had small influence on localization accuracy. The case study supported simulation results. Conclusion: Reliable source reconstruction derived from ECoG can be achieved by the application of the MUSIC algorithm. Linear estimation needs additional compensation mechanisms. Significance: MUSIC based 3D localization based on ECoG has the potential improving epilepsy diagnosis and cognitive research. © 2009 International Federation of Clinical Neurophysiology.
46. De Peralta, R.G., O. Hauk, and S.L. Gonzalez, The neuroelectromagnetic inverse problem and the zero dipole localization error. Computational Intelligence and Neuroscience, 2009. 2009.
Summary: A tomography of neural sources could be constructed from EEG/MEG recordings once the neuroelectromagnetic inverse problem (NIP) is solved. Unfortunately the NIP lacks a unique solution and therefore additional constraints are needed to achieve uniqueness. Researchers are then confronted with the dilemma of choosing one solution on the basis of the advantages publicized by their authors. This study aims to help researchers to better guide their choices by clarifying what is hidden behind inverse solutions oversold by their apparently optimal properties to localize single sources. Here, we introduce an inverse solution (ANA) attaining perfect localization of single sources to illustrate how spurious sources emerge and destroy the reconstruction of simultaneously active sources. Although ANA is probably the simplest and robust alternative for data generated by a single dominant source plus noise, the main contribution of this manuscript is to show that zero localization error of single sources is a trivial and largely uninformative property unable to predict the performance of an inverse solution in presence of simultaneously active sources. We recommend as the most logical strategy for solving the NIP the incorporation of sound additional a priori information about neural generators that supplements the information contained in the data. Copyright © 2009 Rolando Grave de Peralta et al.
47. Daunizeau, J., S.J. Kiebel, and K.J. Friston, Dynamic causal modelling of distributed electromagnetic responses. NeuroImage, 2009. 47(2): p. 590-601.
Summary: In this note, we describe a variant of dynamic causal modelling for evoked responses as measured with electroencephalography or magnetoencephalography (EEG and MEG). We depart from equivalent current dipole formulations of DCM, and extend it to provide spatiotemporal source estimates that are spatially distributed. The spatial model is based upon neural-field equations that model neuronal activity on the cortical manifold. We approximate this description of electrocortical activity with a set of local standing-waves that are coupled though their temporal dynamics. The ensuing distributed DCM models source as a mixture of overlapping patches on the cortical mesh. Time-varying activity in this mixture, caused by activity in other sources and exogenous inputs, is propagated through appropriate lead-field or gain-matrices to generate observed sensor data. This spatial model has three key advantages. First, it is more appropriate than equivalent current dipole models, when real source activity is distributed locally within a cortical area. Second, the spatial degrees of freedom of the model can be specified and therefore optimised using model selection. Finally, the model is linear in the spatial parameters, which finesses model inversion. Here, we describe the distributed spatial model and present a comparative evaluation with conventional equivalent current dipole (ECD) models of auditory processing, as measured with EEG. © 2009 Elsevier Inc. All rights reserved.
48. Cuspineda Bravo, E.R., C. Machado, T. Virues, E. Martínez-Montes, A. Ojeda, P.A. Valdés, J. Bosch, and L. Valdes, Source analysis of alpha rhythm reactivity using LORETA imaging with 64-channel EEG and individual MRI. Clinical EEG and Neuroscience, 2009. 40(3): p. 150-156.
Summary: Conventional EEG and quantitative EEG visual stimuli (close-open eyes) reactivity analysis have shown their usefulness in clinical practice; however studies at the level of EEG generators are limited. The focus of the study was visual reactivity of cortical resources in healthy subjects and in a stroke patient. The 64 channel EEG and T1 magnetic resonance imaging (MRI) studies were obtained from 32 healthy subjects and a middle cerebral artery stroke patient. Low Resolution Electromagnetic Tomography (LORETA) was used to estimate EEG sources for both close eyes (CE) vs. open eyes (OE) conditions using individual MRI. The t-test was performed between source spectra of the two conditions. Thresholds for statistically significant t values were estimated by the local false discovery rate (lfdr) method. The Z transform was used to quantify the differences in cortical reactivity between the patient and healthy subjects. Closed-open eyes alpha reactivity sources were found mainly in posterior regions (occipito-parietal zones), extended in some cases to anterior and thalamic regions. Significant cortical reactivity sources were found in frequencies different from alpha (lower t-values). Significant changes at EEG reactivity sources were evident in the damaged brain hemisphere. Reactivity changes were also found in the "healthy" hemisphere when compared with the normal population. In conclusion, our study of brain sources of EEG alpha reactivity provides information that is not evident in the usual topographic analysis.
49. Catena, A., G. Houghton, B. Valdés, and L.J. Fuentes, Unmasking word processing with ERPs: Two novel linear techniques for the estimation of temporally overlapped waveforms. Brain Topography, 2009. 22(1): p. 60-71.
Summary: Masked priming experiments are frequently used to study automatic aspects of word processing. Direct measures of such processing obtained with functional neuroimaging techniques (ERPs, fMRI, etc.) need to isolate the neural activation related to relevant events when they are rapidly followed by others (a situation found in other popular paradigms such as the attentional blink and repetition blindness). Here we examine the assumption of "simple insertion", which underlies the use of subtraction to isolate components of temporally overlapping waveforms. We propose two novel linear methods and illustrate how they extract temporal and spatial ERP components that the subtraction method fails to detect. We show this through the analysis of ERP data from a masked semantic priming procedure. The new techniques reveal activation generated by unconscious (masked) prime words as early as 100 ms and 200 ms post stimulus-onset; a pattern which simple subtraction fails to detect. © 2009 Springer Science+Business Media, LLC.
50. Buján, A., M. Lindín, and F. Díaz, Movement related cortical potentials in a face naming task: Influence of the tip-of-the-tongue state. International Journal of Psychophysiology, 2009. 72(3): p. 235-245.
Summary: The aim of the present study was evaluate the movement-related cortical potentials (MRCPs) associated with manual and speech movements during a face naming task carried out by the same participants as in a previous study, in order to: 1) determine whether the slowing down of the reaction time observed in the tip-of-the-tongue (TOT) state was caused by motor processes; 2) compare the MRCPs among the three response categories (tip-of-the-tongue, successful retrieval and not knowing the name); and 3) determine whether the MRCPs modulated the differences in amplitude of the late negative wave among response categories. The first component of readiness potential, the negative slope, the motor potential and the reafferent potential associated with the manual response, and two components associated with the verbal responses-the speech-related motor potential and the speech-related reafferent potential-were identified. The slowing down of reaction time observed in the TOT category may be due to a temporal interruption in the motor programming of the responses due to the TOT state. The longer latency in speech-related components in the KNOW with respect to the TOT category can be attributed to the greater cognitive demands involved in the retrieval of proper names in the former category. The brain activity associated with the preparation and execution of the responses had a differential modulatory effect on the amplitude of the LNW component, which may partially explain the differences between the categories observed in the previous study by Díaz et al. [Díaz, F., Lindín, M., Galdo-Álvarez, S., Facal, D., Juncos-Rabadán, O., 2007. An event-related potentials study of face identification and naming: the tip-of-the-tongue state. Psychophysiology 44, 50-68]. © 2008 Elsevier B.V. All rights reserved.
51. Brem, S., P. Halder, K. Bucher, P. Summers, E. Martin, and D. Brandeis, Tuning of the visual word processing system: Distinct developmental ERP and fMRI effects. Human Brain Mapping, 2009. 30(6): p. 1833-1844.
Summary: Visual tuning for words vs. symbol strings yields complementary increases of fast occipito-temporal activity (N1 or N170) in the event-related potential (ERP), and posterior-anterior gradients of increasing word-specific activity with functional magnetic resonance imaging (fMRI) in the visual word form system (VWFS). However, correlation of these coarse ERP and fMRI tuning responses seems limited to the most anterior part of the VWFS in adult and adolescent readers (Brem et al. : Neuroimage 29:822-837). We thus focused on fMRI tuning gradients of young readers with their more pronounced ERP print tuning, and compared developmental aspects of ERP and fMRI response tuning in the VWFS. Children (10.3 y, n = 19), adolescents (16.2 y, n = 13) and adults (25.2 y, n = 18) were tested with the same implicit reading paradigm using counterbalanced ERP and fMRI imaging. The word-specific occipito-temporal N1 specialization, its corresponding source activity, as well as the integrated source activity (0-700 ms) were most prominent in children and showed a marked decrease with age. The posterior-anterior fMRI gradient of word-specific activity instead which was fully established in children did not develop further, but exhibited a dependence on reading skills independent of age. To conclude, prominent developmental dissociation of the ERP and fMRI tuning patterns emerged despite convergent VWFS localization. The ERP response may selectively reflect fast visual aspects of print specialization, which become less important with age, while the fMRI response seems dominated by integrated task- and reading-related activations in the same regions. © 2009 Wiley-Liss, Inc.
52. Bradberry, T.J., F. Rong, and J.L. Contreras-Vidal, Decoding center-out hand velocity from MEG signals during visuomotor adaptation. NeuroImage, 2009. 47(4): p. 1691-1700.
Summary: During reaching or drawing, the primate cortex carries information about the current and upcoming position of the hand. Researchers have decoded hand position, velocity, and acceleration during center-out reaching or drawing tasks from neural recordings acquired invasively at the microscale and mesoscale levels. Here we report that we can continuously decode information about hand velocity at the macroscale level from magnetoencephalography (MEG) data acquired from the scalp during a center-out drawing task with an imposed hand-cursor rotation. The grand mean (n = 5) correlation coefficients (CCs) between measured and decoded velocity profiles were 0.48, 0.40, 0.38, and 0.28 for the horizontal dimension of movement and 0.32, 0.49, 0.56, and 0.23 for the vertical dimension of movement where the order of the CCs indicates pre-exposure, early-exposure, late-exposure, and post-exposure to the hand-cursor rotation. By projecting the sensor contributions to decoding onto whole-head scalp maps, we found that a macroscale sensorimotor network carries information about detailed hand velocity and that contributions from sensors over central and parietal scalp areas change due to adaptation to the rotated environment. Moreover, a 3-D linear estimation of distributed current sources using standardized low-resolution brain electromagnetic tomography (sLORETA) permitted a more detailed investigation into the cortical network that encodes for hand velocity in each of the adaptation phases. Beneficial implications of these findings include a non-invasive methodology to examine the neural correlates of behavior on a macroscale with high temporal resolution and the potential to provide continuous, complex control of a non-invasive neuromotor prosthesis for movement-impaired individuals. © 2009 Elsevier Inc. All rights reserved.
53. Boehler, C.N., J.K. Tsotsos, M.A. Schoenfeld, H.J. Heinze, and J.M. Hopf, The center-surround profile of the focus of attention arises from recurrent processing in visual cortex. Cerebral Cortex, 2009. 19(4): p. 982-991.
Summary: We recently demonstrated with magnetoencephalographic recordings in human observers that the focus of attention in visual search has a spatial profile consisting of a center enhancement surrounded by a narrow zone of sensory attenuation. Here, we report new data from 2 experiments providing insights into the cortical processes that cause the surround attenuation. We show that surround suppression appears in search tasks that require spatial scrutiny, that is the precise binding of search-relevant features at the target's location but not in tasks that permit target discrimination without precise localization. Furthermore, we demonstrate that surround attenuation is linked with a stronger recurrent activity modulation in early visual cortex. Finally, we show that surround suppression appears with a delay (more than 175 ms) that is beyond the time course of the initial feedforward sweep of processing in the visual system. These observations together indicate that the suppressive surround is associated with recurrent processing and binding in the visual cortex.
54. Belardinelli, P., L. Ciancetta, M. Staudt, V. Pizzella, A. Londei, N. Birbaumer, G.L. Romani, and C. Braun, Motor control in young patients with unilateral brain lesions: An MEG study. Cognitive Processing, 2009. 10(SUPPL. 2).
55. Babiloni, C., C. Del Percio, P.M. Rossini, N. Marzano, M. Iacoboni, F. Infarinato, R. Lizio, M. Piazza, M. Pirritano, G. Berlutti, G. Cibelli, and F. Eusebi, Judgment of actions in experts: A high-resolution EEG study in elite athletes. NeuroImage, 2009. 45(2): p. 512-521.
Summary: The present study tested the two following hypotheses: (i) compared to non-athletes, elite athletes are characterized by a reduced cortical activation during the judgment of sporting observed actions; (ii) in elite athletes, a good judgment of observed sporting actions is related to a low cortical activation. To address these issues, electroencephalographic (EEG) data were recorded in 15 elite rhythmic gymnasts and 13 non-gymnasts. They observed a series of 120 rhythmic gymnastic videos. At the end of each video, the subjects had to judge the artistic/athletic level of the exercise by a scale from 0 to 10. The mismatch between their judgment and that of the coach indexed the degree of action judgment. The EEG cortical sources were estimated by sLORETA. With reference to a pre-stimulus period, the power decrease of alpha (8-12 Hz) rhythms during the videos indexed the cortical activation (event related desynchronization, ERD). Regarding the hypothesis (i), low- and high-frequency alpha ERD was lower in amplitude in the elite rhythmic gymnasts compared to the non-gymnasts in occipital and temporal areas (ventral pathway) and in dorsal pathway. Regarding the hypothesis (ii), in the elite rhythmic gymnasts high-frequency alpha ERD was higher in amplitude with the videos characterized by a high judgment error than those characterized by a low judgment error; this was true in inferior posterior parietal and ventral premotor areas ("mirror" pathway). These results globally suggest that the judgment of observed sporting actions is related to low amplitude of alpha ERD, as a possible index of spatially selective cortical activation ("neural efficiency"). © 2008 Elsevier Inc. All rights reserved.
56. Alp, Y.K., O. Arikan, and S. Karakas, ERP source reconstruction by using Particle Swarm Optimization. ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings, 2009: p. 365-368.
Summary: Localization of the sources of Event Related Potentials (ERP) is a challenging inverse problem, especially to resolve sources of neural activity occurring simultaneously. By using an effective dipole source model, we propose a new technique for accurate source localization of ERP signals. The parameters of the dipole ERP sources are optimally chosen by using Particle Swarm Optimization technique. Obtained results on synthetic data sets show that proposed method well localizes the dipoles on their actual locations. On real data sets, the fit error between the actual and reconstructed data is successfully reduced to noise level by localizing a few dipoles in the brain. ©2009 IEEE.
57. Zumer, J.M., H.T. Attias, K. Sekihara, and S.S. Nagarajan, Probabilistic algorithms for MEG/EEG source reconstruction using temporal basis functions learned from data. NeuroImage, 2008. 41(3): p. 924-940.
Summary: We present two related probabilistic methods for neural source reconstruction from MEG/EEG data that reduce effects of interference, noise, and correlated sources. Both methods localize source activity using a linear mixture of temporal basis functions (TBFs) learned from the data. In contrast to existing methods that use predetermined TBFs, we compute TBFs from data using a graphical factor analysis based model [Nagarajan, S.S., Attias, H.T., Hild, K.E., Sekihara, K., 2007a. A probabilistic algorithm for robust interference suppression in bioelectromagnetic sensor data. Stat Med 26, 3886-3910], which separates evoked or event-related source activity from ongoing spontaneous background brain activity. Both algorithms compute an optimal weighting of these TBFs at each voxel to provide a spatiotemporal map of activity across the brain and a source image map from the likelihood of a dipole source at each voxel. We explicitly model, with two different robust parameterizations, the contribution from signals outside a voxel of interest. The two models differ in a trade-off of computational speed versus accuracy of learning the unknown interference contributions. Performance in simulations and real data, both with large noise and interference and/or correlated sources, demonstrates significant improvement over existing source localization methods. © 2008 Elsevier Inc. All rights reserved.
58. Zariffa, J. and M.R. Popovic, Solution space reduction in the peripheral nerve source localization problem using forward field similarities. Journal of Neural Engineering, 2008. 5(2): p. 191-202.
Summary: Improving our ability to localize bioelectric sources within a peripheral nerve would help us to monitor the control signals flowing to and from any limb or organ. This technology would provide a useful neuroscience tool, and could perhaps be incorporated into a neuroprosthesis interface. We propose to use measurements from a multi-contact nerve cuff to solve an inverse problem of bioelectric source localization within the peripheral nerve. Before the inverse problem can be addressed, the forward problem is solved using finite element modeling. A fine mesh improves the accuracy of the forward problem solution, but increases the number of variables to be solved for in the inverse problem. To alleviate this problem, variables corresponding to mesh elements that are not distinguishable by the measurement setup are grouped together, thus reducing the dimension of the inverse problem without impacting on the forward problem accuracy. A quantitative criterion for element distinguishability is derived using the columns of the leadfield matrix and information about the uncertainty in the measurements. Our results indicate that the number of variables in the inverse problem can be reduced by more than half using the proposed method, without having a detrimental impact on the quality of the localization. © 2008 IOP Publishing Ltd.
59. Zariffa, J. and M.R. Popovic, Application of EEG source localization algorithms to the monitoring of active pathways in peripheral nerves. Proceedings of the 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS'08 - "Personalized Healthcare through Technology", 2008: p. 4216-4219.
Summary: Improved techniques for identifying active pathways in peripheral nerves using extraneural measurements would have numerous applications in the fields of neuroprostheses, neural system engineering, and diagnostics. In this study, we propose to approach this issue as an inverse problem of bioelectric source localization, using measurements from a multi-contact nerve cuff electrode. This problem is a modified version of the electroencephalogram/magneto-encephalogram (EEG/MEG) source localization problem. We therefore evaluate the performance of two well-known EEG/MEG source localization algorithms, namely sLORETA and sFOCUSS, when they are applied to the peripheral nerve problem. sLORETA is found to be a potentially viable approach, albeit with limited resolution, while sFOCUSS is found to produce too many spurious pathways in the presence of noise. © 2008 IEEE.
60. Xu, P., Y. Tian, X. Lei, X. Hu, and D. Yao, Equivalent charge source model based iterative maximum neighbor weight for sparse EEG source localization. Annals of Biomedical Engineering, 2008. 36(12): p. 2051-2067.
Summary: How to localize the neural electric activities within brain effectively and precisely from the scalp electroencephalogram (EEG) recordings is a critical issue for current study in clinical neurology and cognitive neuroscience. In this paper, based on the charge source model and the iterative re-weighted strategy, proposed is a new maximum neighbor weight based iterative sparse source imaging method, termed as CMOSS (Charge source model based Maximum neighbOr weight Sparse Solution). Different from the weight used in focal underdetermined system solver (FOCUSS) where the weight for each point in the discrete solution space is independently updated in iterations, the new designed weight for each point in each iteration is determined by the source solution of the last iteration at both the point and its neighbors. Using such a new weight, the next iteration may have a bigger chance to rectify the local source location bias existed in the previous iteration solution. The simulation studies with comparison to FOCUSS and LORETA for various source configurations were conducted on a realistic 3-shell head model, and the results confirmed the validation of CMOSS for sparse EEG source localization. Finally, CMOSS was applied to localize sources elicited in a visual stimuli experiment, and the result was consistent with those source areas involved in visual processing reported in previous studies. © 2008 Biomedical Engineering Society.
61. Wydenkeller, S., R. Wirz, and P. Halder, Spinothalamic tract conduction velocity estimated using contact heat evoked potentials: What needs to be considered. Clinical Neurophysiology, 2008. 119(4): p. 812-821.
Summary: Objective: Laser-evoked potentials have been shown to be clinically useful for the electrophysiological assessment of nociceptive pathways. Contact heat evoked potentials (CHEP) are less established but might be advantageous for clinical purposes. This study aimed at determining the conduction velocity (CV) of central pain (spinothalamic tract, STT) pathways using contact heat stimulation in order to replicate previous findings using laser stimulation. Methods: Contact heat stimulation 3 °C higher than the pain threshold was applied at different body locations in 20 subjects. Results: The CHEP latencies correlated significantly with the respective pain thresholds. Without normalization for this effect no significant linear regression between distance to the brain and the latencies was found. Conversely, if thresholds were considered, the regression was significant and the CV of the STT (ranging between 11.2 and 13.4 m/s) was comparable to CVs estimated after laser stimulation. Conclusions: Pain thresholds seem crucial in interpreting CHEP latencies. It is suggested that the rather low heating rate is responsible for the dependence of latencies on the pain thresholds. Significance: This study shows the importance of pain thresholds and their control to attain valid CV of the STT after contact heat stimulation in healthy subjects. © 2007 International Federation of Clinical Neurophysiology.
62. Wieser, H.G., Psychopathology in epileptology. Psychopathologie in der epileptologie, 2008. 159(5): p. 317-330.
Summary: The observation of positive and negative seizure symptoms in the context of focal epileptic seizures represents a window to the brain, in particular if the localisation of the epileptic discharge can be accurately and reliably determined. The epileptic local dysfunction which gives rise to the aura of an epileptic patient represents a bridge between neurology and psychiatry because it can be viewed as short-lived (or in the case of aura continua or dyscognitive limbic status epilepticus as an extended) ictal psychosis. Of particular interest are complex epileptic hallucinations due to discharges in the limbic system because they are frequently associated with changes in the emotional and affective sphere as well as with mood changes. Epileptic de novo hallucinations often cannot be adequately described by patients because there exist no such phenomena in the real outer world. In the context of presurgical evaluation of possible candidates of epilepsy surgery direct recording and electrical stimulation of the brain have provided fascinating insights. Nowadays the invasive EEG methods are complemented by new and non-invasive functional imaging techniques, such as functional magnetic resonance imaging (fMRI), positron emission tomography (PET) and refined EEG mapping (such as LORETA or related techniques). EEG has the unsurpassable advantage of its excellent time resolution. In addition, focal or regional transitory inactivation of brain structures is possible and indicated in certain patients, as is the case in the so-called "selective temporal lobe amobarbital memory test" to predict postoperative memory outcome in patients in whom a selective therapeutic removal of amygdala and hippocampus is planned. Finally, important insights and impulses for modern brain research have emerged from the analysis of the sequels of therapeutic epilepsy surgeries, such as the so-called split-brain symptomatology observed as a consequence of total corpus callosum section. In this article we comment on some aspects of consciousness and awareness. We concentrate on the epileptic aura and epileptic hallucinations and illustrate some electroclinical findings. Aura continua and dyscognitive limbic status epilepticus as ictal phenomena and the interictal behavioural syndrome of temporal lobe epilepsy are referred to. Because auras most often represent memory flashbacks, some memory subsystems and their main brain substrates and the selective inactivation of medial temporal lobe structures by injection of amobarbital into the territory of the anterior choroidal artery are introduced and briefly discussed.
63. Van Den Doel, K., U.M. Ascher, and D.K. Pai, Computed myography: Three-dimensional reconstruction of motor functions from surface EMG data. Inverse Problems, 2008. 24(6).
Summary: We describe a methodology called computed myography to qualitatively and quantitatively determine the activation level of individual muscles by voltage measurements from an array of voltage sensors on the skin surface. A finite element model for electrostatics simulation is constructed from morphometric data. For the inverse problem, we utilize a generalized Tikhonov regularization. This imposes smoothness on the reconstructed sources inside the muscles and suppresses sources outside the muscles using a penalty term. Results from experiments with simulated and human data are presented for activation reconstructions of three muscles in the upper arm (biceps brachii, bracialis and triceps). This approach potentially offers a new clinical tool to sensitively assess muscle function in patients suffering from neurological disorders (e.g., spinal cord injury), and could more accurately guide advances in the evaluation of specific rehabilitation training regimens. © 2008 IOP Publishing Ltd.
64. Van Den Doel, K., U.M. Ascher, A. Curt, J. Steeves, and D.K. Pai, Computed myography (CMG): Three dimensional reconstruction of motor functions from surface EMG data. Proceedings of the 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS'08 - "Personalized Healthcare through Technology", 2008: p. 550-554.
Summary: We describe a methodology to qualitatively and quantitatively determine the activation level of individual muscles by voltage measurements from an array of voltage sensors on the skin surface. A physical finite element model for electrostatics simulation is constructed from morphometric data and numerical inversion techniques are used to determine muscle activation patterns. Preliminary results from experiments with simulated and human data are presented for activation reconstructions of three muscles in the upper arm (biceps brachii, bracialis, and triceps). This approach potentially offers a new clinical tool to sensitively assess muscle function in patients suffering from neurological disorders (e.g., spinal cord injury) and could more accurately guide advances in the evaluation of specific rehabilitation training regimens. © 2008 IEEE.
65. Trujillo-Barreto, N.J., E. Aubert-Vázquez, and W.D. Penny, Bayesian M/EEG source reconstruction with spatio-temporal priors. NeuroImage, 2008. 39(1): p. 318-335.
Summary: This article proposes a Bayesian spatio-temporal model for source reconstruction of M/EEG data. The usual two-level probabilistic model implicit in most distributed source solutions is extended by adding a third level which describes the temporal evolution of neuronal current sources using time-domain General Linear Models (GLMs). These comprise a set of temporal basis functions which are used to describe event-related M/EEG responses. This places M/EEG analysis in a statistical framework that is very similar to that used for PET and fMRI. The experimental design can be coded in a design matrix, effects of interest characterized using contrasts and inferences made using posterior probability maps. Importantly, as is the case for single-subject fMRI analysis, trials are treated as fixed effects and the approach takes into account between-trial variance, allowing valid inferences to be made on single-subject data. The proposed probabilistic model is efficiently inverted by using the Variational Bayes framework under a convenient mean-field approximation (VB-GLM). The new method is tested with biophysically realistic simulated data and the results are compared to those obtained with traditional spatial approaches like the popular Low Resolution Electromagnetic TomogrAphy (LORETA) and minimum variance Beamformer. Finally, the VB-GLM approach is used to analyze an EEG data set from a face processing experiment. © 2007 Elsevier Inc. All rights reserved.
66. Tomkins, O., I. Shelef, I. Kaizerman, A. Eliushin, Z. Afawi, A. Misk, M. Gidon, A. Cohen, D. Zumsteg, and A. Friedman, Blood-brain barrier disruption in post-traumatic epilepsy. Journal of Neurology, Neurosurgery and Psychiatry, 2008. 79(7): p. 774-777.
Summary: Background: Traumatic brain injury (TBI) is an important cause of focal epilepsy. Animal experiments indicate that disruption of the blood-brain barrier (BBB) plays a critical role in the pathogenesis of post-traumatic epilepsy (PTE). Objective: To investigate the frequency, extent and functional correlates of increased BBB permeability in patient with PTE. Methods: 32 head trauma patients were included in the study, with 17 suffering from PTE. Patients underwent brain MRI (bMRI) and were evaluated for BBB disruption, using a novel semi-quantitative technique. Cortical dysfunction was measured using electroencephalography (EEG), and localised using standardised low-resolution brain electromagnetic tomography (sLORETA). Results: Spectral EEG analyses revealed significant slowing in patients with TBI, with no significant differences between patients with epilepsy and those without. Although bMRI revealed that patients with PTE were more likely to present with intracortical lesions (p = 0.02), no differences in the size of the lesion were found between the groups (p = 0.19). Increased BBB permeability was found in 76.9% of patients with PTE compared with 33.3% of patients without epilepsy (p = 0.047), and could be observed years following the trauma. Cerebral cortex volume with BBB disruption was larger in patients with PTE (p = 0.001). In 70% of patients, slow (delta band) activity was co-localised, by sLORETA, with regions showing BBB disruption. Conclusions: Lasting BBB pathology is common in patients with mild TBI, with increased frequency and extent being observed in patients with PTE. A correlation between disrupted BBB and abnormal neuronal activity is suggested.
67. Terakawa, Y., N. Tsuyuguchi, H. Tanaka, Y. Shigihara, S. Sakamoto, T. Takami, and K. Ohata, Quantitative analysis of MEG using modified sLORETA for clinical application. Clinical Neurophysiology, 2008. 119(8): p. 1917-1922.
Summary: Objective: To determine whether standardised low-resolution brain electromagnetic tomography modified for a quantifiable method (sLORETA-qm) can be used for quantitative analysis in magnetoencephalography (MEG). Methods: Somatosensory evoked fields (SEFs) were obtained from 10 hemispheres of five healthy volunteers stimulated on the median nerve at 0.75, 1.0, 1.25, 1.5, 1.75 and 2.0 × threshold of thenar muscle twitch (TMT). N20m intensity changes were analysed quantitatively using sLORETA-qm. Then, SEFs were measured with stimulation on the median nerve at 1.5 × TMT from 47 hemispheres in 24 subjects. sLORETA-qm intensity and the equivalent current dipole (ECD) moment of N20m were calculated, and relationships between the values were evaluated. Results: sLORETA-qm intensity increased linearly with stimulus intensity between 0.75 and 1.5 × TMT, and tended to reach a plateau or decrease at higher stimulus intensities. The distribution of sLORETA-qm intensity after natural logarithmic transformation was normal and a close correlation was found between the ECD moment and sLORETA-qm intensity (rs = 0.91, p < 0.001). Conclusions: The results of this study focusing on N20m suggested that sLORETA-qm is reliable for quantitative analysis of MEG as well as ECD models. Significance: sLORETA-qm appears promising for quantitative analyses of MEG for which ECD models are inappropriate. © 2008 International Federation of Clinical Neurophysiology.
68. Tapia, M., L. Carretié, B. Sierra, and F. Mercado, Incidental encoding of emotional pictures: Affective bias studied through event related brain potentials. International Journal of Psychophysiology, 2008. 68(3): p. 193-200.
Summary: Emotional stimuli are better remembered than neutral stimuli. Most of the studies taking into account this emotional bias refer to explicit memory, use behavioral measures of the recall and predict better recall of negative stimuli. The few studies taking into account implicit memory and the valence emotional dimension are inconclusive on the effect of the stimulus' emotional valence. In the present study, 120 pictures (30 positive, 30 negative, 30 relaxing and 30 neutral) were shown to, and assessed by, 28 participants (study phase). Subsequently, event related brain potentials (ERPs) were recorded during the presentation of 120 new (shown for the first time) and 120 old (already shown in the study phase) pictures (test phase). No explicit instructions or clues related to recovery were given to participants, and a distractor task was employed, in order to maintain implicit the memory assessment. As expected from other studies' data, our results showed that old stimuli elicited an enhanced late positive component 450 ms after stimulus onset (repetition effect). Moreover, this effect was modulated by the stimuli's emotional valence, since the most positively valenced stimuli were associated with a decreased repetition effect with respect to the most negatively valenced stimuli. This effect was located at ventromedial prefrontal cortex. These results suggest the existence of a valence-mediated bias in implicit memory. © 2008 Elsevier B.V. All rights reserved.
69. Tanaka, H., T. Kimura, A. Kodabashi, T. Fujimoto, M. Usui, K. Takeuchi, T. Matsumoto, Y. Higashi, M. Sekine, and T. Tamura, Evaluation of MEG source estimation using a phantom which is also capable of detecting source location of anatomical images. Proceedings of the IEEE/EMBS Region 8 International Conference on Information Technology Applications in Biomedicine, ITAB, 2008: p. 247-250.
Summary: Cerebral nerve activity estimated by means of Magnetoencephalography (MEG) is usually evaluated by fusion with anatomical images such as MRI, X-ray CT. Therefore, in order to diagnose using MEG measurement results, it is very important to consider not only accuracy of MEG source estimation but also total accuracy including fusion with these anatomical images. In this report, we introduce a phantom which is capable of detecting the source location from these anatomical images as well as MEG measurement, and show this phantom can be used for the evaluation of MEG source estimation including fusion with anatomical images. © 2008 IEEE.
70. Spyrou, L. and S. Sanei, Source localization of event-related potentials incorporating spatial notch filters. IEEE Transactions on Biomedical Engineering, 2008. 55(9): p. 2232-2239.
Summary: A novel algorithm for the localization of event-related potential (ERP) sources within the brain is proposed here. In this technique, spatial notch filters are developed to exploit the multichannel electroencephalogram data together with a model of ERP with variable parameters in order to accurately localize the corresponding ERP signal sources. The algorithm is robust in the presence of reasonably high noise. The performance of the proposed system has been compared to that of linear constrained minimum variance (LCMV) beamformer for different noise and correlation levels and its superiority has been demonstrated. © 2006 IEEE.
71. Šóš, P., M. Brunovský, J. Horáček, M. Bareš, and M. Kopeček, Utilization of cordance analysis and electromagnetic tomography in monitoring changes of electric brain activity during depressive disorder treatment. Využití kordanční analýzy a elektromagnetické tomografie ke sledování změn elektrické mozkové aktivity během léčby depresivní poruchy, 2008. 12(3): p. 167-171.
Summary: The case report of a depressed patient demonstrates the use of QEEG information in the prediction of a treatment response to an antidepressant and possibly of the maintenance of this response. Resting EEG record of depressive patient, having responded to the new antidepressive treatment (venlafaxine), was analyzed after 1, 4 and 14 weeks using the methods of quantitative electroencephalography (QEEG): cordance analysis and electromagnetic tomography (sLORETA - standardized Low-Resolution Electromagnetic Tomography). Decrease in prefrontal EEG theta cordance was found after the first week of treatment (by the time, when no clinical evidence of improvement was apparent) and the response sustainment correlated with increasing and spreading trend of theta activity (4-8 Hz) current density in dorsal cingulum.
72. Schneider, S., V. Brümmer, H.K. Strüder, H. Carnahan, and C.D. Askew, Alteration of electro-cortical activity in microgravity. European Space Agency, (Special Publication) ESA SP, 2008. 663 SP.
Summary: There is growing interest in the effects of weightlessness on central nervous system (CNS) activity. Due to technical and logistical limitations it presently seems impossible to apply imaging techniques as fMRI or PET in weightless environments e.g. on ISS or during parabolic flights. Within this study we evaluated changes in brain cortical activity using low resolution brain electromagnetic tomography (LORETA) during parabolic flights. Results showed a distinct inhibition of right frontal area activity >12Hz during phases of microgravity compared to normal gravity. We conclude that the inhibition of high frequency frontal activity during microgravity may serve as a marker of emotional anxiety and/or indisposition associated with weightlessness. This puts a new light on the debate as to whether cognitive and sensorimotor impairments are attributable to primary physiological effects or secondary psychological effects of a weightless environment.
73. Schneider, S., V. Brümmer, H. Carnahan, A. Dubrowski, C.D. Askew, and H.K. Strüder, What happens to the brain in weightlessness? A first approach by EEG tomography. NeuroImage, 2008. 42(4): p. 1316-1323.
Summary: Basic changes in environmental conditions are fundamental to understanding brain cortical mechanisms. Several studies have reported impairment of central nervous processes during weightlessness. There is ongoing debate as to whether these impairments are attributable to primary physiological effects or secondary psychological effects of the weightlessness environment. This study evaluates the physiological effects of changed gravity conditions on brain cortical activity. In a first experiment, EEG activity of seven participants was recorded at normal, increased and zero gravity during a parabolic flight. Additionally an EEG under normal gravity conditions preflight was recorded. In a second experiment, 24 participants were exposed to a supine, seated and 9° head-down tilt position while EEG was recorded. Data were analysed using low resolution brain electromagnetic tomography (LORETA). Beta-2 EEG activity (18-35 Hz) was found to be increased in the right superior frontal gyrus under normal gravity conditions inflight. By exposure to weightlessness a distinct inhibition of this activity within the same areas could be noticed. As the tilt experiment showed changes in the left inferior temporal gyrus in supine and tilted positions we conclude that the observed changes under weightlessness are not explainable by hemodynamic changes but rather reflect emotional processes related to the experience of weightlessness. These findings suggest that weightlessness has a major impact on electro cortical activity and may affect central nervous and adaptation processes. © 2008 Elsevier Inc.
74. Pratt, H., A. Starr, H.J. Michalewski, N. Bleich, and N. Mittelman, The auditory P50 component to onset and offset of sound. Clinical Neurophysiology, 2008. 119(2): p. 376-387.
Summary: Objective: The auditory Event-Related Potentials (ERP) of component P50 to sound onset and offset have been reported to be similar, but their magnetic homologue has been reported absent to sound offset. We compared the spatio-temporal distribution of cortical activity during P50 to sound onset and offset, without confounds of spectral change. Methods: ERPs were recorded in response to onsets and offsets of silent intervals of 0.5 s (gaps) appearing randomly in otherwise continuous white noise and compared to ERPs to randomly distributed click pairs with half second separation presented in silence. Subjects were awake and distracted from the stimuli by reading a complicated text. Measures of P50 included peak latency and amplitude, as well as source current density estimates to the clicks and sound onsets and offsets. Results: P50 occurred in response to noise onsets and to clicks, while to noise offset it was absent. Latency of P50 was similar to noise onset (56 ms) and to clicks (53 ms). Sources of P50 to noise onsets and clicks included bilateral superior parietal areas. In contrast, noise offsets activated left inferior temporal and occipital areas at the time of P50. Source current density was significantly higher to noise onset than offset in the vicinity of the temporo-parietal junction. Conclusions: P50 to sound offset is absent compared to the distinct P50 to sound onset and to clicks, at different intracranial sources. P50 to stimulus onset and to clicks appears to reflect preattentive arousal by a new sound in the scene. Sound offset does not involve a new sound and hence the absent P50. Significance: Stimulus onset activates distinct early cortical processes that are absent to offset. © 2007 International Federation of Clinical Neurophysiology.
75. Perchet, C., F. Godinho, S. Mazza, M. Frot, V. Legrain, M. Magnin, and L. Garcia-Larrea, Evoked potentials to nociceptive stimuli delivered by CO2 or Nd:YAP lasers. Clinical Neurophysiology, 2008. 119(11): p. 2615-2622.
Summary: Objective: This study compares the amplitude, latency, morphology, scalp topography and intracranial generators of laser-evoked potentials (LEPs) to CO2 and Nd:YAP laser stimuli. Methods: LEPs were assessed in 11 healthy subjects (6 men, mean age 39 ± 10 years) using a 32-channel acquisition system. Laser stimuli were delivered on the dorsum of both hands (intensity slightly above pain threshold), and permitted to obtain lateralised (N1) and vertex components (N2-P2) with similar scalp distribution for both types of lasers. Results: The N1-YAP had similar latencies but significantly higher amplitudes relative to N1-CO2. The N2-P2 complex showed earlier latencies, higher amplitudes (N2) and more synchronised responses when using Nd:YAP stimulation. The distribution of intracranial generators assessed with source localization analyses (sLORETA) was similar for Nd:YAP and CO2 lasers. The insular, opercular, and primary sensorimotor cortices were active during the N1 time-window, whereas the anterior midcingulate, supplementary motor areas and mid-anterior insulae were active concomitant to the N2-P2 complex. Conclusions: Earlier latencies and larger amplitudes recorded when using Nd:YAP pulses suggest a more synchronized nociceptive afferent volley with this type of laser. Significance: This, together with its handy utilization due to optic fibre transmission, may favour the use of Nd:YAP lasers in clinical settings. © 2008 International Federation of Clinical Neurophysiology.
76. Olivares-Carreño, E.I. and J. Iglesias-Dorado, Long-latency evoked potentials and mnemonic processing of faces and words. Potenciales evocados de larga latencia y procesamiento mnésico de caras y palabras, 2008. 47(12): p. 624-630.
Summary: Introduction. Evoked potentials are real-time electrophysiological markers of cognitive operations and especially mnemonic processes. The N400 wave has traditionally been studied to characterise the processes involved in memorising verbal material. To investigate the existence of specific memory processes for each information domain, functional analogues of this wave were examined during the processing of non-verbal stimuli, such as faces. Aim. Using an inter-subject design, the classic verbal N400 wave was compared with its functional analogue during the processing of faces in a contextual preactivation task adapted to the visual domain of faces. Subjects and methods. After several sessions dedicated to learning a set of faces, another evoked potential recording session was held in order to analyse the effects of the existence of structural inconsistencies in these stimuli and to compare them, with regard to their topographic distribution and neural generators, with those observed in the classic verbal N400 task. Results. A verbal N400 wave was observed with a (slightly right) centroparietal distribution, and this response was distinguished from another negative wave obtained during the processing of facial inconsistencies in the same group of participants, with a predominantly occipital localisation and differentiated neural generators. Conclusions. These findings support the hypothesis of the specificity of the neural mechanisms involved in the mnemonic processing of faces and words, which is in line with the neurocognitive models that suggest the independence or modularity of memory processes in different domains of information. © 2008, Revista de Neurología.
77. Nir, R.R., R. Lev, R. Moont, Y. Granovsky, E. Sprecher, and D. Yarnitsky, Neurophysiology of the Cortical Pain Network: Revisiting the Role of S1 in Subjective Pain Perception Via Standardized Low-Resolution Brain Electromagnetic Tomography (sLORETA). Journal of Pain, 2008. 9(11): p. 1058-1069.
Summary: Multiple studies have supported the usefulness of standardized low-resolution brain electromagnetic tomography (sLORETA) in localizing generators of scalp-recorded potentials. The current study implemented sLORETA on pain event-related potentials, primarily aiming at validating this technique for pain research by identifying well-known pain-related regions. Subsequently, we pointed at investigating the still-debated and ambiguous topic of pain intensity coding at these regions, focusing on their relative impact on subjective pain perception. sLORETA revealed significant activations of the bilateral primary somatosensory (SI) and anterior cingulate cortices and of the contralateral operculoinsular and dorsolateral prefrontal (DLPFC) cortices (P < .05 for each). Activity of these regions, excluding DLPFC, correlated with subjective numerical pain scores (P < .05 for each). However, a multivariate regression analysis (R = .80; P = .024) distinguished the contralateral SI as the only region whose activation magnitude significantly predicted the subjective perception of noxious stimuli (P = .020), further substantiated by a reduced regression model (R = .75, P = .008). Based on (1) correspondence of the pain-activated regions identified by sLORETA with the acknowledged imaging-based pain-network and (2) the contralateral SI proving to be the most contributing region in pain intensity coding, we found sLORETA to be an appropriate tool for relevant pain research and further substantiated the role of SI in pain perception. Perspective: Because the literature of pain intensity coding offers inconsistent findings, the current article used a novel tool for revisiting this controversial issue. Results suggest that it is the activation magnitude of SI, which solely establishes the significant correlation with subjective pain ratings, in accordance with the classical clinical thinking, relating SI lesions to diminished perception of pain. Although this study cannot support a causal relation between SI activation magnitude and pain perception, such relation might be insinuated. © 2008 American Pain Society.
78. Millán, J.D.R., P.W. Ferrez, F. Galán, E. Lew, and R. Chavarriaga, Non-invasive brain-machine interaction. International Journal of Pattern Recognition and Artificial Intelligence, 2008. 22(5): p. 959-972.
Summary: The promise of Brain-Computer Interfaces (BCI) technology is to augment human capabilities by enabling interaction with computers through a conscious and spontaneous modulation of the brainwaves after a short training period. Indeed, by analyzing brain electrical activity online, several groups have designed brain-actuated devices that provide alternative channels for communication, entertainment and control. Thus, a person can write messages using a virtual keyboard on a computer screen and also browse the internet. Alternatively, subjects can operate simple computer games, or brain games, and interact with educational software. Work with humans has shown that it is possible for them to move a cursor and even to drive a wheelchair. This paper briefly reviews the field of BCI, with a focus on noninvasive systems based on electroencephalogram (EEG) signals. It also describes three brain-actuated devices we have developed: a virtual keyboard, a brain game, and a wheelchair. Finally, it shortly discusses current research directions we are pursuing in order to improve the performance and robustness of our BCI system, especially for real-time control of brain-actuated robots. © 2008 World Scientific Publishing Company.
79. McDonald, J.J. and J.J. Green, Isolating event-related potential components associated with voluntary control of visuo-spatial attention. Brain Research, 2008. 1227(C): p. 96-109.
Summary: Attention-directing cues presented at fixation evoke several lateralized event-related potential (ERP) components prior to the onset of visual targets. These components have been associated with the control of visuo-spatial attention, but the neuro-cognitive operations and neural generators of the components are still largely unknown. Here, we isolated cue-elicited ERP activity in different ways to home in on different neuro-cognitive operations and to gain a better understanding about the possible neuroanatomical sources of the cue-elicited ERP activities. To isolate lateralized cue-ERP activity, we compared shift-left and shift-right cue ERPs to shift-up cue ERPs. To measure all of the ERP activity related to attentional control, including spatially nonspecific activity that is removed in the process of isolating lateralized cue-ERP components, we compared shift-cue ERPs to neutral-cue (i.e., no-shift) ERPs. Isolated lateralized-ERP activity was seen in the contralateral-occipital lobe in the early phase of the cue-target interval and in the ipsilateral-occipital lobe in the late phase. The later, ipsilateral activity indicates that the late directing attention positivity (LDAP) reflected processing of the to-be-ignored location. The neutral-cue isolation revealed a shift-related positivity over posterior scalp regions and a shift-related negativity over more anterior scalp regions. The spatio-temporal sequence of shift-related activity observed on the scalp, together with estimates of distributed source activity underlying the shift-related ERP components, indicated that frontal and parietal regions of cortex participated in the control of attention and led to pre-target biasing in visual cortical areas. © 2008 Elsevier B.V. All rights reserved.
80. Lorenzo-López, L., E. Amenedo, R.D. Pascual-Marqui, and F. Cadaveira, Neural correlates of age-related visual search decline: A combined ERP and sLORETA study. NeuroImage, 2008. 41(2): p. 511-524.
Summary: Differences in the neural systems underlying visual search processes for young (n = 17, mean age 19.6 ± 1.9) and older (n = 22, mean age 68.5 ± 6) subjects were investigated combining the Event-Related Potential (ERP) technique with standardized Low-Resolution brain Electromagnetic Tomography (sLORETA) analyses. Behavioral results showed an increase in mean reaction times (RTs) and a reduction in hit rates with age. The ERPs were significantly different between young and older subjects at the P3 component, showing longer latencies and lower amplitudes in older subjects. These ERP results suggest an age-related decline in the intensity and speed of visual processing during visual search that imply a reduction in attentional resources with normal aging. The sLORETA data revealed a significantly reduced neural differentiation in older subjects, who recruited bilateral prefrontal regions in a nonselective manner for the different search arrays. Finally, sLORETA between-group comparisons revealed that relative to young subjects, older subjects showed significantly reduced activity in anterior cingulate cortex as well as in numerous limbic and occipitotemporal regions contributing to visual search processes. These findings provide evidence that the neural circuit supporting this cognitive process is vulnerable to normal aging. All these attentional factors could contribute to poorer performance of older compared to young subjects in visual search tasks. © 2008 Elsevier Inc. All rights reserved.
81. Leal, A.J.R., A.I. Dias, J.P. Vieira, A. Moreira, L. Távora, and E. Calado, Analysis of the dynamics and origin of epileptic activity in patients with tuberous sclerosis evaluated for surgery of epilepsy. Clinical Neurophysiology, 2008. 119(4): p. 853-861.
Summary: Objective: The epilepsies associated with the tuberous sclerosis complex (TSC) are very often refractory to medical therapy. Surgery for epilepsy is an effective alternative when the critical link between the localization of seizure onset in the scalp and a particular cortical tuber can be established. In this study we perform analysis of ictal and interictal EEG to improve such link. Methods: The ictal and interictal recordings of four patients with TSC undergoing surgery for epilepsy were submitted to independent component analysis (ICA), followed by source analysis, using the sLORETA algorithm. The localizations obtained for the ictal EEG and for the average interictal spikes were compared. Results: The ICA of ictal EEG produced consistent results in different events, and there was good agreement with the tubers that were successfully removed in three of the four patients (one patient refused surgery). In some patients there was a large discrepancy between the localization of ictal and interictal sources. The interictal activity produced more widespread source localizations. Conclusions: The use of ICA of ictal EEG followed by the use of source analysis methods in four cases of epilepsy and TSC was able to localize the epileptic generators very near the lesions successfully removed in surgery for epilepsy. Significance: The ICA of ictal EEG events may be a useful add-on to the tools used to establish the connection between epileptic scalp activity and the cortical tubers originating it, in patients with TSC considered for surgery of epilepsy. © 2007 International Federation of Clinical Neurophysiology.
82. Krusemark, E.A., W. Keith Campbell, and B.A. Clementz, Attributions, deception, and event related potentials: An investigation of the self-serving bias. Psychophysiology, 2008. 45(4): p. 511-515.
Summary: Self-serving attributions occur when negative personal outcomes are ascribed to external circumstances and when positive outcomes are ascribed to internal factors. Individuals strategically employ the self-serving bias to maintain and protect positive self-views. The current study investigated the neural correlates of the self-serving bias using dense array EEG, giving 20 participants false (success or failure) feedback during a facial working memory task. Participants made self-serving attributions during the task, primarily following failure feedback. Voltage and source analyses in response to attribution stimuli revealed that, compared to self-serving responses, non-self-serving attributions were preceded by enhanced dorsomedial frontal cortex activity. This finding suggests that unbiased attributions require greater self-control, overriding the automatic tendency for self-enhancement. Copyright © 2008 Society for Psychophysiological Research.
83. Kim, M.S., J.S. Kim, and C.K. Chung, Neural correlates of immediate and delayed word recognition memory: An MEG study. Brain Research, 2008. 1240(C): p. 132-142.
Summary: We investigated the neural correlates of immediate and delayed word recognition memory using whole head magnetoencephalography (MEG). Event-related potential (ERP) and event-related field (ERF) were simultaneously recorded from 10 subjects while performing a continuous recognition memory task. Subjects were required to determine whether the word was "new" (never before presented) or "old" (presented previously). Old items were presented either immediately or delayed with five intervening words, and the words presented only once were referred to as new words. The grand average ERP waveform showed that immediate repetition was associated with early P300 and absence of N400, while delayed repetition and new word were associated with late P300 and presence of N400. Three ERF components were observed for immediate repetition, while four components were observed for delayed repetition and new word conditions. M1 and M2 were observed across all stimulus-presentation conditions. M3 with medial temporal generators was observed only in delayed repetition and new word conditions. M4 was observed earlier in the immediate repetition than in the delayed repetition and new-word conditions. For M4 generators, cingulate gyrus activations were observed for all stimulus-presentation conditions. In addition, activations in the medial temporal areas were observed for both repetition conditions. These results suggest that immediate and delayed recognition memory have similar neural networks except for the additional involvement of medial temporal areas in delayed recognition memory. The functional roles of M3 and M4 peaks were discussed in terms of functional significance of N400 and early/late P300 ERP peaks, which correspond to M3 and M4, respectively. © 2008 Elsevier B.V. All rights reserved.
84. Kim, J.S., J.M. Han, K.S. Park, and C.K. Chung, Distribution-based minimum-norm estimation with multiple trials. Computers in Biology and Medicine, 2008. 38(11-12): p. 1203-1210.
Summary: The goal of this study is to develop a source imaging method for electroencephalography and magnetoencephalography by analyzing a distance measure based on a Euclidean norm of difference between pre- and post-stimulus brain activities. Conventional source imaging techniques generally detect evoked responses by averaging multiple trials at each source point. These methods are limited in their ability to fully analyze complex brain signals with a mixture of evoked and induced activities because they compare means or variances. In this article, we propose a novel approach for eliciting significant evoked and induced activity. To this aim, response and baseline ranges from each trial are separately mapped in an anatomically constrained source space by minimum-norm estimation. The extent within a distribution and the distance between distributions of brain activities at each source point are estimated from the set of trials. Then, this distance analysis determines the degree of difference between the response and baseline activities. The statistical significance of the distance comparison was computed using a nonparametric permutation test. In the evaluation of simulated data sets, the proposed method provided robust images of the simulated location (p<0.05), whereas the average method did not detect the perturbed source. A total of 200 randomly selected locations were tested with a signal-to-noise ratio (SNR) of 2 dB, and the error between simulated points and the maximum-value-points analyzed using this method was 9±15 mm. © 2008 Elsevier Ltd. All rights reserved.
85. Kim, J.S. and C.K. Chung, Language lateralization using MEG beta frequency desynchronization during auditory oddball stimulation with one-syllable words. NeuroImage, 2008. 42(4): p. 1499-1507.
Summary: Some patients with epilepsy have difficulty performing complex language tasks due to the long duration of the disease and cognitive side effects of antiepileptic drugs. Therefore, a simple passive paradigm would be useful for determining the language dominance lateralization in epilepsy patients. The goal of this study was to develop an efficient and non-invasive analysis method for determining language dominance in epilepsy patients. To this end, magnetoencephalography was performed while an auditory stimulus sequence comprised of two one-syllable spoken words was presented to 17 subjects in an oddball paradigm without subject response. The time-frequency difference between deviant and standard sounds was then analyzed in the source space using a spatial filtering method that was based on minimum-norm estimation. The laterality index was estimated in language-related regions of interest (ROI). The results were compared to the traditional lateralization method using the Wada test. Beta band oscillation activity decreased during deviant stimulation, and the lateralization of the decrease was in good agreement with the Wada test, in the posterior part of the inferior frontal gyrus in 94% of the subjects and in the posterior part of the superior temporal gyrus in 71% of the subjects. In conclusion, the ROI-based time-frequency difference between deviant and standard sounds can be used to assess language lateralization in accordance with the Wada test. © 2008 Elsevier Inc.
86. Khemakhem, R., A.B. Hamida, A. Ahmed-Taleb, and P. Derambure, New hybrid method for the 3D reconstruction of neuronal activity in the brain. Proceedings of IWSSIP 2008 - 15th International Conference on Systems, Signals and Image Processing, 2008: p. 405-408.
Summary: Estimation of the electrical cartography on the scalp surface requires a solution to the EEG inverse problem, but, there is no unique solution to this problem. In this paper we present Standardized LOw Resolution brain Electromagnetic TomogrAphy "sLORETA", the FOCaI Underdetermined System Solver "FOCUSS", and the new combination solution "sLORET A-FOCUSS" methods. The purpose of this paper is to present the technical details of these methods, and give some comparison between them. The results demonstrate that using each method, we obtain different results given the reconstruction in 3D of the cerebral activity in the brain from where we evaluate the efficiency of the sLORETA-FOCUSS method to reconstruct a three dimensional source distribution with smaller localization and a minimum of localization error.
87. Khemakhem, R., A. Ben Hamida, I. Feki, and A. Taleb-Ahmed, Recursive sLORETA-FOCUSS algorithm for EEG dipoles localization. 2008 1st International Workshops on Image Processing Theory, Tools and Applications, IPTA 2008, 2008.
Summary: The electrical activity inside the brain consists of currents generated by biochemical sources at cellular level. This activity can be measured by an electroencephalography. Neurologists have been interested in determining the location of the epileptogenic zones from measured potential on the scalp in order to avoid invasive techniques. The problem is recognizing by inverse problem. In this paper we propose an amelioration of the inverse problem method "sLORETA-FOCUSS" given by smoothing the current density distribution. We present a comparative study of the sLORETA-FOCUSS and the new solution named recursive sLORETA-FOCUSS. The found results demonstrate that the new method is able to give good results in term of localization error, simulated time, and precision of reconstruction in 3D. © 2008 IEEE.
88. Jann, K., R. Wiest, M. Hauf, K. Meyer, C. Boesch, J. Mathis, G. Schroth, T. Dierks, and T. Koenig, BOLD correlates of continuously fluctuating epileptic activity isolated by independent component analysis. NeuroImage, 2008. 42(2): p. 635-648.
Summary: Combined EEG/fMRI recordings offer a promising opportunity to detect brain areas with altered BOLD signal during interictal epileptic discharges (IEDs). These areas are likely to represent the irritative zone, which is itself a reflection of the epileptogenic zone. This paper reports on the imaging findings using independent component analysis (ICA) to continuously quantify epileptiform activity in simultaneously acquired EEG and fMRI. Using ICA derived factors coding for the epileptic activity takes into account that epileptic activity is continuously fluctuating with each spike differing in amplitude, duration and maybe topography, including subthreshold epileptic activity besides clear IEDs and may thus increase the sensitivity and statistical power of combined EEG/fMRI in epilepsy. Twenty patients with different types of focal and generalized epilepsy syndromes were investigated. ICA separated epileptiform activity from normal physiological brain activity and artifacts. In 16/20 patients, BOLD correlates of epileptic activity matched the EEG sources, the clinical semiology, and, if present, the structural lesions. In clinically equivocal cases, the BOLD correlates aided to attribute proper diagnosis of the underlying epilepsy syndrome. Furthermore, in one patient with temporal lobe epilepsy, BOLD correlates of rhythmic delta activity could be employed to delineate the affected hippocampus. Compared to BOLD correlates of manually identified IEDs, the sensitivity was improved from 50% (10/20) to 80%. The ICA EEG/fMRI approach is a safe, non-invasive and easily applicable technique, which can be used to identify regions with altered hemodynamic effects related to IEDs as well as intermittent rhythmic discharges in different types of epilepsy. © 2008 Elsevier Inc. All rights reserved.
89. Huber, R., S. Määttä, S.K. Esser, S. Sarasso, F. Ferrarelli, A. Watson, F. Ferreri, M.J. Peterson, and G. Tononi, Measures of cortical plasticity after transcranial paired associative stimulation predict changes in electroencephalogram slow-wave activity during subsequent sleep. Journal of Neuroscience, 2008. 28(31): p. 7911-7918.
Summary: Sleep slow-wave activity (SWA) is thought to reflect sleep need, increasing in proportion to the previous time awake and decreasing during sleep, although the underlying mechanisms are unclear. Recent studies have shown that procedures presumably leading to local plastic changes in the cerebral cortex can lead to local changes in SWA during subsequent sleep. To further investigate the connection between cortical plasticity and sleep SWA, in this study we used a paired associative stimulation (PAS) protocol, in which median nerve stimuli were followed at different intervals (25 or 10 ms) by transcranial magnetic stimulation (TMS) pulses to the contralateral cortical hand area. As expected, such a protocol led to a sustained increase (long-term potentiation-like) or decrease (long-term depression-like) of cortical excitability as measured by motor evoked potentials. By using a TMS-compatible high-density electroencephalographic (EEG) system, we also found that, in individual subjects, TMS-evoked cortical responses over sensorimotor cortex changed with different interstimulus intervals. Moreover, during subsequent sleep, SWA increased locally in subjects whose TMS-evoked cortical responses had increased after PAS, and decreased in subjects whose cortical responses had decreased. Changes in TMS-evoked cortical EEG response and change in sleep SWA were localized to similar cortical regions and were positively correlated. Together, these results suggest that changes in cortical excitability in opposite directions lead to corresponding changes in local sleep regulation, as reflected by SWA, providing evidence for a tight relationship between cortical plasticity and sleep intensity. Copyright © 2008 Society for Neuroscience.
90. Hofmann, M.J., S. Tamm, M.M. Braun, M. Dambacher, A. Hahne, and A.M. Jacobs, Conflict monitoring engages the mediofrontal cortex during nonword processing. NeuroReport, 2008. 19(1): p. 25-29.
Summary: The current study investigated the role played by conflict monitoring in a lexical-decision task involving competing word representations, using event-related potentials. We extended the multiple read-out model (Grainger and Jacobs, 1996), a connectionist model of word recognition, to quantify conflict by means of Hopfield Energy, which is defined as the sum of the products of all orthographic word node pair activations within the artificial mental lexicon of this model. With increasing conflict levels in nonwords, a late negativity increased in amplitude (400-600 ms) accompanied by activation of the anterior cingulate cortex and the medial frontal gyrus. The simulated conflict predicted the amplitudes associated with this mediofrontal conflict-monitoring network on an item level, and is consistent with the conflict-monitoring theory. © 2008 Lippincott Williams & Wilkins, Inc.
91. Haufe, S., V.V. Nikulin, A. Ziehe, K.R. Müller, and G. Nolte, Combining sparsity and rotational invariance in EEG/MEG source reconstruction. NeuroImage, 2008. 42(2): p. 726-738.
Summary: We introduce Focal Vector Field Reconstruction (FVR), a novel technique for the inverse imaging of vector fields. The method was designed to simultaneously achieve two goals: a) invariance with respect to the orientation of the coordinate system, and b) a preference for sparsity of the solutions and their spatial derivatives. This was achieved by defining the regulating penalty function, which renders the solutions unique, as a global ℓ1-norm of local ℓ2-norms. We show that the method can be successfully used for solving the EEG inverse problem. In the joint localization of 2-3 simulated dipoles, FVR always reliably recovers the true sources. The competing methods have limitations in distinguishing close sources because their estimates are either too smooth (LORETA, Minimum ℓ1-norm) or too scattered (Minimum ℓ2-norm). In both noiseless and noisy simulations, FVR has the smallest localization error according to the Earth Mover's Distance (EMD), which is introduced here as a meaningful measure to compare arbitrary source distributions. We also apply the method to the simultaneous localization of left and right somatosensory N20 generators from real EEG recordings. Compared to its peers FVR was the only method that delivered correct location of the source in the somatosensory area of each hemisphere in accordance with neurophysiological prior knowledge. © 2008 Elsevier Inc. All rights reserved.
92. Hamani, C., M.P. McAndrews, M. Cohn, M. Oh, D. Zumsteg, C.M. Shapiro, R.A. Wennberg, and A.M. Lozano, Memory enhancement induced by hypothalamic/fornix deep brain stimulation. Annals of Neurology, 2008. 63(1): p. 119-123.
Summary: Bilateral hypothalamic deep brain stimulation was performed to treat a patient with morbid obesity. We observed, quite unexpectedly, that stimulation evoked detailed autobiographical memories. Associative memory tasks conducted in a double-blinded "on" versus "off" manner demonstrated that stimulation increased recollection but not familiarity-based recognition, indicating a functional engagement of the hippocampus. Electroencephalographic source localization showed that hypothalamic deep brain stimulation drove activity in mesial temporal lobe structures. This shows that hypothalamic stimulation in this patient modulates limbic activity and improves certain memory functions. © 2007 American Neurological Association.
93. Guardiera, S. and S. Schneider, The interaction of motor performance and psychophysiological effects during acceleration to hypergravity. European Space Agency, (Special Publication) ESA SP, 2008. 663 SP.
Summary: Several studies reported that human motor performance is impaired during acceleration to hypergravity. While physiological explanations (e.g. vestibular activity) are widely discussed, psycho-physiological reasons (e.g. stress) are less considered. The present study therefore evaluates the interaction between psycho-physiological effects and motor performance in hypergravity. Eleven subjects performed a manual tracking task. Additionally, stress hormone concentration, EEG and subjective mood were evaluated. All measurements were performed in normal (+1Gz), and in (or directly after) three times gravitational acceleration (+3Gz). Motor performance decreased, while all determined stress hormone concentrations increased in +3Gz. EEG analysis revealed an increase of brain cortical activity in right frontal lobe in +3Gz. Subjective mood decreased due to +3Gz. Our data confirm, that motor performance is decreased in hypergravity, whereas an increase in sychophysiological stress markers could be obtained. We conclude that psycho-physiological changes have to be regarded as a possible explanation for deficits in motor performance in hypergravity.
94. Green, J.J., J.A. Conder, and J.J. McDonald, Lateralized frontal activity elicited by attention-directing visual and auditory cues. Psychophysiology, 2008. 45(4): p. 579-587.
Summary: In event-related potential studies of voluntary spatial attention, lateralized activity observed over anterior scalp sites prior to an impending target has been interpreted as the activity of a supramodal attentional control mechanism in the frontal lobes. However, variability in the scalp topography and presence of this activity across studies suggests that multiple neural generators contribute to the lateralized activity recorded at the scalp. Using distributed source modeling we found two distinct frontal lobe sources following attention-directing cues, one dependent on the sensory modality of the eliciting stimulus and one dependent on the response requirements of the task. Differential activity of these sources depending on task parameters suggests that neither source reflects activity necessary for controlling attention. Copyright © 2008 Society for Psychophysiological Research.
95. Grech, R., T. Cassar, J. Muscat, K.P. Camilleri, S.G. Fabri, M. Zervakis, P. Xanthopoulos, V. Sakkalis, and B. Vanrumste, Review on solving the inverse problem in EEG source analysis. Journal of NeuroEngineering and Rehabilitation, 2008. 5.
Summary: In this primer, we give a review of the inverse problem for EEG source localization. This is intended for the researchers new in the field to get insight in the state-of-the-art techniques used to find approximate solutions of the brain sources giving rise to a scalp potential recording. Furthermore, a review of the performance results of the different techniques is provided to compare these different inverse solutions. The authors also include the results of a Monte-Carlo analysis which they performed to compare four non parametric algorithms and hence contribute to what is presently recorded in the literature. An extensive list of references to the work of other researchers is also provided. This paper starts off with a mathematical description of the inverse problem and proceeds to discuss the two main categories of methods which were developed to solve the EEG inverse problem, mainly the non parametric and parametric methods. The main difference between the two is to whether a fixed number of dipoles is assumed a priori or not. Various techniques falling within these categories are described including minimum norm estimates and their generalizations, LORETA, sLORETA, VARETA, S-MAP, ST-MAP, Backus-Gilbert, LAURA, Shrinking LORETA FOCUSS (SLF), SSLOFO and ALF for non parametric methods and beamforming techniques, BESA, subspace techniques such as MUSIC and methods derived from it, FINES, simulated annealing and computational intelligence algorithms for parametric methods. From a review of the performance of these techniques as documented in the literature, one could conclude that in most cases the LORETA solution gives satisfactory results. In situations involving clusters of dipoles, higher resolution algorithms such as MUSIC or FINES are however preferred. Imposing reliable biophysical and psychological constraints, as done by LAURA has given superior results. The Monte-Carlo analysis performed, comparing WMN, LORETA, sLORETA and SLF, for different noise levels and different simulated source depths has shown that for single source localization, regularized sLORETA gives the best solution in terms of both localization error and ghost sources. Furthermore the computationally intensive solution given by SLF was not found to give any additional benefits under such simulated conditions. © 2008 Grech et al; licensee BioMed Central Ltd.
96. Gilley, P.M., A. Sharma, and M.F. Dorman, Cortical reorganization in children with cochlear implants. Brain Research, 2008. 1239(C): p. 56-65.
Summary: Congenital deafness leads to atypical organization of the auditory nervous system. However, the extent to which auditory pathways reorganize during deafness is not well understood. We recorded cortical auditory evoked potentials in normal hearing children and in congenitally deaf children fitted with cochlear implants. High-density EEG and source modeling revealed principal activity from auditory cortex in normal hearing and early implanted children. However, children implanted after a critical period of seven years revealed activity from parietotemporal cortex in response to auditory stimulation, demonstrating reorganized cortical pathways. Reorganization of central auditory pathways is limited by the age at which implantation occurs, and may help explain the benefits and limitations of implantation in congenitally deaf children. © 2008 Elsevier B.V. All rights reserved.
97. Ganis, G. and H.E. Schendan, Visual mental imagery and perception produce opposite adaptation effects on early brain potentials. NeuroImage, 2008. 42(4): p. 1714-1727.
Summary: Event-related potentials (ERPs) were recorded during a rapid adaptation paradigm to determine whether visual perception and visual mental imagery of faces recruit the same early perceptual processes. The early effect of face and object adaptors, either perceived or visualized, on test stimuli, was assessed by measuring the amplitude of the N170/VPP complex, typically much larger for faces than for other object categories. Faces elicited a robust N170/VPP complex, localized to posterior ventrolateral occipitotemporal cortex. Both visualized and perceived adaptors affected the N170/VPP complex to test faces from 120 ms post-stimulus, reflecting effects on neural populations supporting early perceptual face categorization. Critically, while perceived adaptors suppressed the amplitude of the N170/VPP, visualized adaptors enhanced it. We suggest that perceived adaptors affect neural populations in the neocortex supporting early perceptual processing of faces via bottom-up mechanisms, whereas visualized adaptors affect them via top-down mechanisms. Similar enhancement effects were found on the N170/VPP complex to non-face objects, suggesting such effects are a general consequence of visual imagery on processing of faces and other object categories. These findings support image-percept equivalence theories and may explain, in part, why visual percepts and visual mental images are not routinely confused, even though both engage similar neural populations in the visual system. © 2008 Elsevier Inc.
98. Galka, A., T. Ozaki, H. Muhle, U. Stephani, and M. Siniatchkin, A data-driven model of the generation of human EEG based on a spatially distributed stochastic wave equation. Cognitive Neurodynamics, 2008. 2(2): p. 101-113.
Summary: We discuss a model for the dynamics of the primary current density vector field within the grey matter of human brain. The model is based on a linear damped wave equation, driven by a stochastic term. By employing a realistically shaped average brain model and an estimate of the matrix which maps the primary currents distributed over grey matter to the electric potentials at the surface of the head, the model can be put into relation with recordings of the electroencephalogram (EEG). Through this step it becomes possible to employ EEG recordings for the purpose of estimating the primary current density vector field, i.e. finding a solution of the inverse problem of EEG generation. As a technique for inferring the unobserved high-dimensional primary current density field from EEG data of much lower dimension, a linear state space modelling approach is suggested, based on a generalisation of Kalman filtering, in combination with maximum-likelihood parameter estimation. The resulting algorithm for estimating dynamical solutions of the EEG inverse problem is applied to the task of localising the source of an epileptic spike from a clinical EEG data set; for comparison, we apply to the same task also a non-dynamical standard algorithm. © 2008 Springer Science+Business Media B.V.
99. Fujimoto, T., A. Kodabashi, M. Usui, K. Takeuchi, T. Otsubo, K. Nakamura, Y. Higashi, K. Kose, H. Tanaka, M. Sekine, and T. Tamura, Normal human brain processing of cold stimulation observed by magneto-encephalography. Proceedings of the IEEE/EMBS Region 8 International Conference on Information Technology Applications in Biomedicine, ITAB, 2008: p. 243-246.
Summary: We investigated the time course of cortical activity in the brain related to cold epidermal touch stimulation at 4degree Celsius and touch stimulation at a normal temperature of 14degree Celsius to the palm of the hand in 20 normal human subjects (average age of 29.1±6.0 years), using magneto-encephalography (MEG). The time course of cortical activities with cold touch stimulation to the right palm showed cortical activities in the posterior portion of the posterior cingulate cortex at an average of 214±101.2 ms before cold touch stimulation, in the ipsilateral somatosensory area at an average of 39.6±37.5 ms, in the contralateral primary somatosensory area at an average of 64.8±28.4 ms, and then in the anterior cingulate cortex, including a portion of the corpus callosum, at an average of 302±126 ms, following cold touch stimulation. It was noted that the time course of cortical activities to cold touch stimulation to the palm showed a difference, compared with normal temperature touch stimulation: cortical activities were observed in the ipsilateral sensory region at an average of 39.6±37.5 ms following cold touch stimulation, but such activities were not observed following normal temperature touch stimulation. On the other hand, there were no significant differences in the time courses of cortical activities in the contralateral primary sensory area and in cingulate regions between the two types of stimulation. The time course of brain activities in response to epidermal stimulation showed no laterality or gender difference. © 2008 IEEE.
100. Friston, K., L. Harrison, J. Daunizeau, S. Kiebel, C. Phillips, N. Trujillo-Barreto, R. Henson, G. Flandin, and J. Mattout, Multiple sparse priors for the M/EEG inverse problem. NeuroImage, 2008. 39(3): p. 1104-1120.
Summary: This paper describes an application of hierarchical or empirical Bayes to the distributed source reconstruction problem in electro- and magnetoencephalography (EEG and MEG). The key contribution is the automatic selection of multiple cortical sources with compact spatial support that are specified in terms of empirical priors. This obviates the need to use priors with a specific form (e.g., smoothness or minimum norm) or with spatial structure (e.g., priors based on depth constraints or functional magnetic resonance imaging results). Furthermore, the inversion scheme allows for a sparse solution for distributed sources, of the sort enforced by equivalent current dipole (ECD) models. This means the approach automatically selects either a sparse or a distributed model, depending on the data. The scheme is compared with conventional applications of Bayesian solutions to quantify the improvement in performance. © 2007 Elsevier Inc. All rights reserved.
101. Fisher, D.J., A. Labelle, and V.J. Knott, The right profile: Mismatch negativity in schizophrenia with and without auditory hallucinations as measured by a multi-feature paradigm. Clinical Neurophysiology, 2008. 119(4): p. 909-921.
Summary: Objective: To examine pre-attentive acoustic change detection in schizophrenia patients with and without auditory hallucinations via mismatch negativity (MMN) extracted from a multi-feature paradigm. Methods: This study examined the electroencephalograph (EEG)-derived MMN, recorded across 32 sites, in 12 hallucinating patients (HPs) with schizophrenia, 12 non-hallucinating patients (NPs) with schizophrenia and 12 healthy controls (HCs). MMN was recorded in response to a multi-feature MMN paradigm [Näätänen, R., et al., 2004. The mismatch negativity (MMN): towards the optimal paradigm. Clin. Neurophys. 115, 140-144] which employs frequency, duration, intensity, location and gap deviants. Differences in source localization were probed using standardized low resolution brain electromagnetic tomography (sLORETA). Results: HPs showed significantly smaller MMNs to duration deviants compared to HCs and NPs, as well as smaller MMNs to intensity deviants compared to HCs. Regionalized differences between HCs and each of the patient groups were observed in response to frequency deviants. There were no significant group effects for location or gap deviants, or for MMN latency. Source localization using sLORETA showed no significant differences in MMN generator location across groups for any of the deviant stimuli. Conclusions: The often-reported robust MMN deficit to duration deviants may be specific to schizophrenia patients afflicted with auditory hallucinations. Furthermore, by using symptom-specific groups, novel deficits of pre-attentive auditory processing, such as that observed to intensity deviants in HPs, may be revealed. Significance: The differential responding observed between both groups of patients with schizophrenia has implications for automatic processing within the auditory cortex of hallucinating patients and suggests that care must be taken when recruiting participants in studies involving schizophrenia to ensure consistent, replicable results. © 2007 International Federation of Clinical Neurophysiology.
102. Ferrez, P.W. and J. Del R. Millán, Error-related EEG potentials generated during simulated brain-computer interaction. IEEE Transactions on Biomedical Engineering, 2008. 55(3): p. 923-929.
Summary: Brain-computer interfaces (BCIs) are prone to errors in the recognition of subject's intent. An elegant approach to improve the accuracy of BCIs consists in a verification procedure directly based on the presence of error-related potentials (ErrP) in the electroencephalogram (EEG) recorded right after the occurrence of an error. Several studies show the presence of ErrP in typical choice reaction tasks. However, in the context of a BCI, the central question is: "Are ErrP also elicited when the error is made by the interface during the recognition of the subject's intent?" We have thus explored whether ErrP also follow a feedback indicating incorrect responses of the simulated BCI interface. Five healthy volunteer subjects participated in a new human-robot interaction experiment, which seem to confirm the previously reported presence of a new kind of ErrP. However, in order to exploit these ErrP, we need to detect them in each single trial using a short window following the feedback associated to the response of the BCI. We have achieved an average recognition rate of correct and erroneous single trials of 83.5% and 79.2%, respectively, using a classifier built with data recorded up to three months earlier. © 2006 IEEE.
103. Ferrarelli, F., M. Massimini, M.J. Peterson, B.A. Riedner, M. Lazar, M.J. Murphy, R. Huber, M. Rosanova, A.L. Alexander, N. Kalin, and G. Tononi, Reduced evoked gamma oscillations in the frontal cortex in schizophrenia patients: A TMS/EEG study. American Journal of Psychiatry, 2008. 165(8): p. 996-1005.
Summary: Objective: Transcranial magnetic stimulation (TMS) combined with high-density electroencephalography (EEG) can be used to directly examine the properties of thalamocortical circuits in the brain without engaging an individual in cognitive or motor tasks. The authors investigated EEG responses in schizophrenia patients and healthy comparison subjects following the application of TMS to the premotor cortex. Method: Sixteen schizophrenia patients and 14 healthy comparison subjects were recruited to participate in the study. Participants underwent three to five TMS/high-density EEG sessions at various TMS doses. The following three aspects of TMS-evoked responses were analyzed: amplitude, synchronization, and source localization. Results: Relative to healthy comparison subjects, schizophrenia patients had a marked decrease in evoked gamma oscillations that occurred within the first 100 msec after TMS, particularly in a cluster of electrodes located in a fronto-central region. These oscillations were significantly reduced in amplitude (calculated using global-mean field power and event-related spectral perturbation analysis) and synchronization (measured using intertrial coherence). Furthermore, source modeling analysis revealed that the TMS-evoked brain activation underlying these gamma oscillations in patients with schizophrenia did not propagate (as it did in healthy comparison subjects) and was mostly confined to the stimulated brain region. Conclusions: Schizophrenia patients showed a decrease in EEG-evoked responses in the gamma band when TMS was applied to directly stimulate the frontal cortex while these responses were recorded. Since EEG responses to direct cortical stimulation are not affected by an individual's motivation, attention, or cognitive capacity and are not relayed through peripheral afferent pathways, these findings suggest that there might be an intrinsic dysfunction in frontal thalamocortical circuits in individuals with schizophrenia.
104. Ding, L. and B. He, Sparse source imaging in electroencephalography with accurate field modeling. Human Brain Mapping, 2008. 29(9): p. 1053-1067.
Summary: We have developed a new L1-norm based generalized minimum norm estimate (GMNE) and have fully characterized the concept of sparseness regularization inherited in the proposed algorithm, which is termed as sparse source imaging (SSI). The new SSI algorithm corrects inaccurate source field modeling in previously reported L1-norm GMNEs and proposes that sparseness a priori should only be applied to the regularization term, not to the data term in the formulation of the regularized inverse problem. A new solver to the newly developed SSI has been adopted and known as the second-order cone programming. The new SSI is assessed by a series of simulations and then evaluated using somatosensory evoked potential (SEP) data with both scalp and subdural recordings in a human subject. The performance of SSI is compared with other L1-norm GMNEs and L2-norm GMNEs using three evaluation metrics, i.e., localization error, orientation error, and strength percentage. The present simulation results indicate that the new SSI has significantly improved performance in all evaluation metrics, especially in the metric of orientation error. L2-norm GMNEs show large orientation errors because of the smooth regularization. The previously reported L1-norm GMNEs show large orientation errors due to the inaccurate source field modeling. The SEP source imaging results indicate that SSI has the best accuracy in the prediction of subdural potential field as validated by direct subdural recordings. The new SSI algorithm is also applicable to MEG source imaging. © 2007 Wiley-Liss, Inc.
105. Dalal, S.S., A.G. Guggisberg, E. Edwards, K. Sekihara, A.M. Findlay, R.T. Canolty, M.S. Berger, R.T. Knight, N.M. Barbaro, H.E. Kirsch, and S.S. Nagarajan, Five-dimensional neuroimaging: Localization of the time-frequency dynamics of cortical activity. NeuroImage, 2008. 40(4): p. 1686-1700.
Summary: The spatiotemporal dynamics of cortical oscillations across human brain regions remain poorly understood because of a lack of adequately validated methods for reconstructing such activity from noninvasive electrophysiological data. In this paper, we present a novel adaptive spatial filtering algorithm optimized for robust source time-frequency reconstruction from magnetoencephalography (MEG) and electroencephalography (EEG) data. The efficacy of the method is demonstrated with simulated sources and is also applied to real MEG data from a self-paced finger movement task. The algorithm reliably reveals modulations both in the beta band (12-30 Hz) and high gamma band (65-90 Hz) in sensorimotor cortex. The performance is validated by both across-subjects statistical comparisons and by intracranial electrocorticography (ECoG) data from two epilepsy patients. Interestingly, we also reliably observed high frequency activity (30-300 Hz) in the cerebellum, although with variable locations and frequencies across subjects. The proposed algorithm is highly parallelizable and runs efficiently on modern high-performance computing clusters. This method enables the ultimate promise of MEG and EEG for five-dimensional imaging of space, time, and frequency activity in the brain and renders it applicable for widespread studies of human cortical dynamics during cognition. © 2008 Elsevier Inc. All rights reserved.
106. Clementz, B.A., J. Wang, and A. Keil, Normal electrocortical facilitation but abnormal target identification during visual sustained attention in schizophrenia. Journal of Neuroscience, 2008. 28(50): p. 13411-13418.
Summary: Attentional deficits in schizophrenia have been investigated using target identification tasks which conflate the abilities to successfully (1) attend to possible target locations and (2) detect target events. Whether compromised attentional selectivity or abnormal target detection causes schizophrenia subjects' poor performance on visual attention tasks, therefore, is unknown. To address this issue, we measured the neural activity (using electroencephalography) of 17 schizophrenia and 17 healthy subjects during a target identification task. Participants viewed superimposed images (horizontal and vertical bars differing in color) and attended to one image to identify bar width changes in specific locations. Bars were frequency tagged so attention directed to unique parts of the images could be tracked. Steady-state visual evoked potentials (ssVEPs) were used to quantify attention-related neural activity to specific parts of the visual images. Behavioral performance and event-related potentials (ERPs) in response to the target events were used to quantify target detection abilities. For both schizophrenia and healthy subjects, attending to specific parts of the attended image enhanced brain activity related to attended bars and reduced activity evoked by unattended bars. Activity in relation to the spatially overlapping unattended image was unaffected. Schizophrenia patients, however, were impaired on target detection abilities on both behavioral and brain activity measures. Target-related behavioral and brain activity measures were highly correlated in both groups. These findings indicate that deficient target detection rather than compromised attentional selectivity accounts for previously reported visual attention deficits in schizophrenia. Copyright © 2008 Society for Neuroscience.
107. Carrillo-de-la-Peña, M.T., S. Galdo-Álvarez, and C. Lastra-Barreira, Equivalent is not equal: Primary motor cortex (MI) activation during motor imagery and execution of sequential movements. Brain Research, 2008. 1226(C): p. 134-143.
Summary: The motor hierarchy hypothesis and the related debate about the role of the primary motor cortex (MI) in motor preparation are major topics in cognitive neuroscience today. The present study combines the two strategies that have been followed to clarify the role of MI in motor preparation independently from execution: motor imagery and the use of precueing tasks. Event-related potentials (ERPs) were recorded while subjects either performed or just imagined sequential finger movements in response to a central target (numbers 1, 2 or 3) which was precued by arrows (at both sides of the screen) that provided information about response side. Both motor imagery and execution elicited Lateralized Readiness Potentials (LRPs) with similar morphology and latency. Given that the LRP is generated in MI, the results show that the primary motor cortex is also active during imagery and give support for the hypothesis of a functional equivalence between motor imagery and execution. Nevertheless, the analysis of the different moments of motor preparation (precue vs. target-induced activity) revealed important differences between both conditions: whereas there were no differences in LRPs nor in brain areas estimated by standardized low resolution tomographies (sLORETA) related to precue presentation, larger LRP amplitudes and higher activation of MI were found during motor execution than imagery in the target-related activity. These results have important implications for the development of brain-computer devices and for the use of motor imagery in neurorehabilitation. © 2008 Elsevier B.V. All rights reserved.
108. Carretié, L., J.A. Hinojosa, J. Albert, S. López-Martín, B.S. De La Gándara, J.M. Igoa, and M. Sotillo, Modulation of ongoing cognitive processes by emotionally intense words. Psychophysiology, 2008. 45(2): p. 188-196.
Summary: Contrary to what occurs with negative pictures, negative words are, in general, not capable of interfering with performance in ongoing cognitive tasks in normal subjects. A probable explanation is the limited arousing power of linguistic material. Especially intense words (insults and compliments), neutral personal adjectives, and pseudowords were presented to 28 participants while they executed a lexical decision task. Insults were associated with the poorest performance in the task and compliments with the best. Amplitude of the late positive component of the event-related potentials, originating at parietal areas, was maximal in response to compliments and insults, but latencies were delayed in response to the latter. Results suggest that intense emotional words modulate ongoing cognitive processes through both bottom-up (attentional capture by insults) and top-down (facilitation of cognitive processing by arousing words) mechanisms. Copyright © 2007 Society for Psychophysiological Research.
109. Cannon, R., J. Lubar, and D. Baldwin, Self-perception and experiential schemata in the addicted brain. Applied Psychophysiology Biofeedback, 2008. 33(4): p. 223-238.
Summary: This study investigated neurophysiological differences between recovering substance abusers (RSA) and controls while electroencephalogram (EEG) was continuously recorded during completion of a new assessment instrument. The participants consisted of 56 total subjects; 28 RSA and 28 non-clinical controls (C). The participants completed the self-perception and experiential schemata assessment (SPESA) and source localization was compared utilizing standardized low-resolution electromagnetic tomography (sLORETA). The data show significant differences between groups during both the assessment condition and baselines. A pattern of alpha activity as estimated by sLORETA was shown in the right amygdala, uncus, hippocampus, BA37, insular cortex and orbitofrontal regions during the SPESA condition. This activity possibly reflects a circuit related to negative perceptions of self formed in specific neural pathways. These pathways may be responsive to the alpha activity induced by many substances by bringing the brain into synchrony if only for a short time. In effect this may represent the euphoria described by substance abusers. © 2008 Springer Science+Business Media, LLC.
110. Bourdaud, N., R. Chavarriaga, F. Gálan, and J.D.R. Millán, Characterizing the EEG correlates of exploratory behavior. IEEE Transactions on Neural Systems and Rehabilitation Engineering, 2008. 16(6): p. 549-556.
Summary: This study aims to characterize the electroencephalography (EEG) correlates of exploratory behavior. Decision making in an uncertain environment raises a conflict between two opposing needs: gathering information about the environment and exploiting this knowledge in order to optimize the decision. Exploratory behavior has already been studied using functional magnetic resonance imaging (fMRI). Based on a usual paradigm in reinforcement learning, this study has shown bilateral activation in the frontal and parietal cortex. To our knowledge, no previous study has been done on it using EEG. The study of the exploratory behavior using EEG signals raises two difficulties. First, the labels of trial as exploitation or exploration cannot be directly derived from the subject action. In order to access this information, a model of how the subject makes his decision must be built. The exploration related information can be then derived from it. Second, because of the complexity of the task, its EEG correlates are not necessarily time locked with the action. So the EEG processing methods used should be designed in order to handle signals that shift in time across trials. Using the same experimental protocol as the fMRI study, results show that the bilateral frontal and parietal areas are also the most discriminant. This strongly suggests that the EEG signal also conveys information about the exploratory behavior. © 2008 IEEE.
111. Boehler, C.N., M.A. Schoenfeld, H.J. Heinze, and J.M. Hopf, Rapid recurrent processing gates awareness in primary visual cortex. Proceedings of the National Academy of Sciences of the United States of America, 2008. 105(25): p. 8742-8747.
Summary: Visual awareness has been proposed to depend on recurrent processing in early visual cortex areas including the primary visual cortex (V1). Here, we address this hypothesis with high spatiotem-poral resolution magnetoencephalographic recordings in subjects performing a substitution masking paradigm. Neural activity reflecting awareness is assessed by directly comparing the neuro-magnetic response elicited by effectively and ineffectively masked targets after the proportion of trials leading to masking was individually adjusted to match the proportion of trials without masking. This revealed a modulation of recurrent activity in the primary visual cortex rapidly after the onset of the feedforward sweep of processing in striate and extrastriate areas but significantly before the onset of attention-dependent recurrent modulations in V1. Our data provide direct support for the notion that (1) recurrent processing in V1 correlates with visual awareness and (2) that attention and awareness involve distinct recurrent processing operations. © 2008 by The National Academy of Sciences of the USA.
112. Beste, C., C. Saft, J. Andrich, R. Gold, and M. Falkenstein, Response inhibition in Huntington's disease-A study using ERPs and sLORETA. Neuropsychologia, 2008. 46(5): p. 1290-1297.
Summary: Huntington's disease (HD) is an autosomal dominant inherited neurodegenerative disorder, with neurodegeneration mainly affecting the striatum. We investigated executive functions related to response inhibition in (HD) and healthy controls by means of event-related potentials (ERP) in a simple Go/Nogo-task. In Nogo as opposed to Go trials two fronto-central ERP components are elicited: the Nogo-N2 and Nogo-P3. These components are supposed to depend on (medial) prefrontal regions, especially the anterior cingulate cortex (ACC). The results show that the Nogo-N2 did not differ between the groups, while the Nogo-P3 demonstrated a strong attenuation in the HD-group, which also showed more false alarms in the Nogo-condition. Using sLORETA it is shown that this attenuation was related to the medial frontal cortex, especially the ACC, and superior frontal cortex areas. Moreover, the attenuation was related to the underlying genetic disease load (CAG-index). The decline in inhibition is likely mediated via a dysfunction in the ACC, which is known to be dysfunctional in HD. Moreover, the results may be interpreted that the decline in response inhibition in HD is gene-associated. The differentially affected Nogo-components suggest that they rely on different neuronal circuits, even within the ACC. For HD this suggests that this structure is not entirely dysfunctional. © 2008 Elsevier Ltd. All rights reserved.
113. Abe, T., K. Ogawa, H. Nittono, and T. Hori, Neural generators of brain potentials before rapid eye movements during human REM sleep: A study using sLORETA. Clinical Neurophysiology, 2008. 119(9): p. 2044-2053.
Summary: Objective: Brain activity preceding rapid eye movements (REM) during human REM sleep has remained poorly understood. Slow negative brain potential (pre-REM negativity) appears before REMs. Current sources of this potential were investigated to identify brain activity immediately preceding REMs. Methods: In this study, 22 young healthy volunteers (20-25 years old) participated. Polysomnograms were recorded during normal nocturnal sleep. Brain potentials between 200 ms before and 50 ms after the onset of REMs and pseudo-triggers (3000 ms before the onset of REMs) were averaged. Standardized low-resolution brain electromagnetic tomography (sLORETA) was used to estimate current sources of pre-REM negativity. Results: Pre-REM negativity appeared with the maximal amplitude at right prefrontal sites immediately before REMs. However, this negativity did not appear before pseudo-triggers. Current sources of the pre-REM negativity were estimated in the ventromedial prefrontal cortex, uncus, insula, anterior cingulated cortex, basal forebrain, parahippocampal gyrus, premotor cortex and frontal eye field. Conclusions: The pre-REM negativity reflects brain activity coupled with the occurrence of REMs. Results of this study suggest that emotion, memory, and motor-related brain activity might occur before REMs. Significance: Pre-REM negativity is expected to be a psychophysiological index for elucidating functions of REM sleep. © 2008 International Federation of Clinical Neurophysiology.
114. Abascal, J.F.P.J., S.R. Arridge, D. Atkinson, R. Horesh, L. Fabrizi, M. De Lucia, L. Horesh, R.H. Bayford, and D.S. Holder, Use of anisotropic modelling in electrical impedance tomography; Description of method and preliminary assessment of utility in imaging brain function in the adult human head. NeuroImage, 2008. 43(2): p. 258-268.
Summary: Electrical Impedance Tomography (EIT) is an imaging method which enables a volume conductivity map of a subject to be produced from multiple impedance measurements. It has the potential to become a portable non-invasive imaging technique of particular use in imaging brain function. Accurate numerical forward models may be used to improve image reconstruction but, until now, have employed an assumption of isotropic tissue conductivity. This may be expected to introduce inaccuracy, as body tissues, especially those such as white matter and the skull in head imaging, are highly anisotropic. The purpose of this study was, for the first time, to develop a method for incorporating anisotropy in a forward numerical model for EIT of the head and assess the resulting improvement in image quality in the case of linear reconstruction of one example of the human head. A realistic Finite Element Model (FEM) of an adult human head with segments for the scalp, skull, CSF, and brain was produced from a structural MRI. Anisotropy of the brain was estimated from a diffusion tensor-MRI of the same subject and anisotropy of the skull was approximated from the structural information. A method for incorporation of anisotropy in the forward model and its use in image reconstruction was produced. The improvement in reconstructed image quality was assessed in computer simulation by producing forward data, and then linear reconstruction using a sensitivity matrix approach. The mean boundary data difference between anisotropic and isotropic forward models for a reference conductivity was 50%. Use of the correct anisotropic FEM in image reconstruction, as opposed to an isotropic one, corrected an error of 24 mm in imaging a 10% conductivity decrease located in the hippocampus, improved localisation for conductivity changes deep in the brain and due to epilepsy by 4-17 mm, and, overall, led to a substantial improvement on image quality. This suggests that incorporation of anisotropy in numerical models used for image reconstruction is likely to improve EIT image quality. © 2008 Elsevier Inc.
115. Zumer, J.M., H.T. Attias, K. Sekihara, and S.S. Nagarajan, A probabilistic algorithm integrating source localization and noise suppression for MEG and EEG data. NeuroImage, 2007. 37(1): p. 102-115.
Summary: We have developed a novel probabilistic model that estimates neural source activity measured by MEG and EEG data while suppressing the effect of interference and noise sources. The model estimates contributions to sensor data from evoked sources, interference sources and sensor noise using Bayesian methods and by exploiting knowledge about their timing and spatial covariance properties. Full posterior distributions are computed rather than just the MAP estimates. In simulation, the algorithm can accurately localize and estimate the time courses of several simultaneously active dipoles, with rotating or fixed orientation, at noise levels typical for averaged MEG data. The algorithm even performs reasonably at noise levels typical of an average of just a few trials. The algorithm is superior to beamforming techniques, which we show to be an approximation to our graphical model, in estimation of temporally correlated sources. Success of this algorithm using MEG data for localizing bilateral auditory cortex, low-SNR somatosensory activations, and for localizing an epileptic spike source are also demonstrated. © 2007 Elsevier Inc. All rights reserved.
116. Zöllig, J., R. West, M. Martin, M. Altgassen, U. Lemke, and M. Kliegel, Neural correlates of prospective memory across the lifespan. Neuropsychologia, 2007. 45(14): p. 3299-3314.
Summary: Overview: Behavioural data reveal an inverted U-shaped function in the efficiency of prospective memory from childhood to young adulthood to later adulthood. However, prior research has not directly compared processes contributing to age-related variation in prospective memory across the lifespan, hence it is unclear whether the same factors explain the 'rise and fall' of prospective remembering from childhood to later adulthood. The present study examined this question using a paradigm that allowed us to consider the behavioural and neural correlates of processes associated with the prospective and retrospective components of prospective memory. Methods: We compared 14 adolescents, 14 young adults, and 14 old adults in a paradigm where the prospective memory task was embedded in a semantic categorization task. Results: The behavioural data revealed an inverted U-shaped function with adolescents and old adults performing poorly relative to young adults. Analyses of the error data revealed that different processes may have contributed to failures of prospective memory in adolescents and older adults. This finding was supported by age differences in ERP-components for cue detection and post-retrieval processes. Additionally, source localization using LORETA revealed different patterns of neural recruitment for adolescents and older adults relative to younger adults. Conclusion: Our findings demonstrate that adolescents and older adults show different patterns of behavioural errors and neural recruitment for successful prospective remembering indicating that different processes may contribute to the 'rise and fall' of prospective memory across the lifespan. © 2007 Elsevier Ltd. All rights reserved.
117. Zhang, J., T. Guo, Y. Xu, X. Zhao, and L. Yao, Spatiotemporal patterns of ERP based on combined ICA-LORETA analysis. Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 2007. 6511(PART 2).
Summary: In contrast to the FMRI methods widely used up to now, this method try to understand more profoundly how the brain systems work under sentence processing task map accurately the spatiotemporal patterns of activity of the large neuronal populations in the human brain from the analysis of ERP data recorded on the brain scalp. In this study, an event-related brain potential (ERP) paradigm to record the on-line responses to the processing of sentences is chosen as an example. In order to give attention to both utilizing the ERPs' temporal resolution of milliseconds and overcoming the insensibility of cerebral location ERP sources, we separate these sources in space and time based on a combined method of independent component analysis (ICA) and low-resolution tomography (LORETA) algorithms. ICA blindly separate the input ERP data into a sum of temporally independent and spatially fixed components arising from distinct or overlapping brain or extra-brain sources. And then the spatial maps associated with each ICA component are analyzed, with use of LORETA to uniquely locate its cerebral sources throughout the full brain according to the assumption that neighboring neurons are simultaneously and synchronously activated. Our results show that the cerebral computation mechanism underlies content words reading is mediated by the orchestrated activity of several spatially distributed brain sources located in the temporal, frontal, and parietal areas, and activate at distinct time intervals and are grouped into different statistically independent components. Thus ICA-LORETA analysis provides an encouraging and effective method to study brain dynamics from ERP.
118. Wagner, M., M. Fuchs, and J. Kastner, SWARM: sLORETA-weighted accurate minimum norm inverse solutions. International Congress Series, 2007. 1300: p. 185-188.
Summary: Standardized Low Resolution Electromagnetic Tomography (sLORETA) localizes the sources of EEG and MEG data with low error. Its outcome, however, is not a distribution of currents modelling brain activity but a statistical map thereof. In this paper, a new inverse method for current density reconstructions from EEG and MEG data is presented. The sLORETA-weighted accurate minimum norm method (SWARM) belongs to the family of weighted minimum norm solutions with its weights based on sLORETA. SWARM localizes point sources with low error, but, unlike sLORETA, it computes a current density vector field. The method is described and its performance is demonstrated for EEG and MEG dipole simulations at different depths. © 2007 Elsevier B.V. All rights reserved.
119. Papageorgiou, C.C., C. Sfagos, K.K. Kosma, K.A. Kontoangelos, N. Triantafyllou, D. Vassilopoulos, A.D. Rabavilas, and C.R. Soldatos, Changes in LORETA and conventional patterns of P600 after steroid treatment in multiple sclerosis patients. Progress in Neuro-Psychopharmacology and Biological Psychiatry, 2007. 31(1): p. 234-241.
Summary: Objective: The P600 component of event-related potentials (ERPs) reflecting the 'rule-governed sequence of information processing', has been associated with multiple sclerosis (MS)-related cognition. The present study aimed at examining the effects of methylprednisolone treatment in MS patients on cognition as reflected by the low-resolution brain electromagnetic tomography (LORETA) of the P600 as well as its conventional constituents (amplitudes and latencies) recorded during a working memory (WM) test. Method: A paired LORETA comparison was performed in the P600 component of ERPs elicited during a (WM) test in 18 MS patients suffering from the relapsing-remitting form, before and after 1 week treatment with methylprednisolone. The P600 component was also evaluated in 16 healthy controls matched to the patients on age and educational level. Results: When pre- and post-treatment recordings of LORETA were compared all patients as a group showed significantly different patterns of current density activation located at right frontal lobe. The treatment was accompanied by an increase of the amplitude of P600 at the right frontoparietal area. In the post-treatment phase the patients exhibited significant improvement of the memory performance as compared to themselves before treatment. As a result both the P600 amplitudes and memory performance at post-treatment were closer to those exhibited by normal controls. Conclusion: These findings support the notion that steroid treatment in relapsing-remitting MS patients, may exert a beneficial effect in 'rule-governed sequence of information processing'. © 2006.
120. Palmero-Soler, E., K. Dolan, V. Hadamschek, and P.A. Tass, swLORETA: A novel approach to robust source localization and synchronization tomography. Physics in Medicine and Biology, 2007. 52(7): p. 1783-1800.
Summary: Standardized low-resolution brain electromagnetic tomography (sLORETA) is a widely used technique for source localization. However, this technique still has some limitations, especially under realistic noisy conditions and in the case of deep sources. To overcome these problems, we present here swLORETA, an improved version of sLORETA, obtained by incorporating a singular value decomposition-based lead field weighting. We show that the precision of the source localization can further be improved by a tomographic phase synchronization analysis based on swLORETA. The phase synchronization analysis turns out to be superior to a standard linear coherence analysis, since the latter cannot distinguish between real phase locking and signal mixing. © 2007 IOP Publishing Ltd.
121. Nummenmaa, A., T. Auranen, M.S. Hämäläinen, I.P. Jääskeläinen, M. Sams, A. Vehtari, and J. Lampinen, Automatic relevance determination based hierarchical Bayesian MEG inversion in practice. NeuroImage, 2007. 37(3): p. 876-889.
Summary: In recent simulation studies, a hierarchical Variational Bayesian (VB) method, which can be seen as a generalisation of the traditional minimum-norm estimate (MNE), was introduced for reconstructing distributed MEG sources. Here, we studied how nonlinearities in the estimation process and hyperparameter selection affect the inverse solutions, the feasibility of a full Bayesian treatment of the hyperparameters, and multimodality of the true posterior, in an empirical dataset wherein a male subject was presented with pure tone and checkerboard reversal stimuli, alone and in combination. An MRI-based cortical surface model was employed. Our results show, with a comparison to the basic MNE, that the hierarchical VB approach yields robust and physiologically plausible estimates of distributed sources underlying MEG measurements, in a rather automated fashion. © 2007 Elsevier Inc. All rights reserved.
122. Nummenmaa, A., T. Auranen, M.S. Hämäläinen, I.P. Jääskeläinen, J. Lampinen, M. Sams, and A. Vehtari, Hierarchical Bayesian estimates of distributed MEG sources: Theoretical aspects and comparison of variational and MCMC methods. NeuroImage, 2007. 35(2): p. 669-685.
Summary: Magnetoencephalography (MEG) provides millisecond-scale temporal resolution for noninvasive mapping of human brain functions, but the problem of reconstructing the underlying source currents from the extracranial data has no unique solution. Several distributed source estimation methods based on different prior assumptions have been suggested for the resolution of this inverse problem. Recently, a hierarchical Bayesian generalization of the traditional minimum norm estimate (MNE) was proposed, in which the variance of distributed current at each cortical location is considered as a random variable and estimated from the data using the variational Bayesian (VB) framework. Here, we introduce an alternative scheme for performing Bayesian inference in the context of this hierarchical model by using Markov chain Monte Carlo (MCMC) strategies. In principle, the MCMC method is capable of numerically representing the true posterior distribution of the currents whereas the VB approach is inherently approximative. We point out some potential problems related to hyperprior selection in the previous work and study some possible solutions. A hyperprior sensitivity analysis is then performed, and the structure of the posterior distribution as revealed by the MCMC method is investigated. We show that the structure of the true posterior is rather complex with multiple modes corresponding to different possible solutions to the source reconstruction problem. We compare the results from the VB algorithm to those obtained from the MCMC simulation under different hyperparameter settings. The difficulties in using a unimodal variational distribution as a proxy for a truly multimodal distribution are also discussed. Simulated MEG data with realistic sensor and source geometries are used in performing the analyses. © 2006 Elsevier Inc. All rights reserved.
123. Marzetti, L., D. Mantini, S. Cugini, G.L. Romani, and C. Del Gratta, High-resolution spatio-temporal neuronal activation in the visual oddball task: A simultaneous EEG/fMRI study. Proc. of 2007 Joint Meet. of the 6th Int. Symp. on Noninvasive Functional Source Imaging of the Brain and Heart and the Int. Conf. on Functional Biomedical Imaging, NFSI and ICFBI 2007, 2007: p. 59-62.
Summary: The combined use of EEG and fMRI allows for the fusion of electrophysiological and hemodynamic information in the study of human cognitive functions. In order to investigate cerebral activity during a visual oddball task, simultaneous EEG/fMRI recording from 10 healthy subjects was performed. A devoted data-analysis method based on trial-by-trial coupling of concurrent EEG and fMRI for the high-resolution spatio-temporal analysis of P300 neuronal activation was developed. Our results obtained from fMRI data showed the involvement of inferior and medial frontal gyrus, cingulated motor area, middle temporal gyrus, and inferior parietal lobule in the oddball task; furthermore, activations were generally right lateralized, in accordance with previous findings. Using the high temporal resolution of EEG, we could separate neuronal activations specifically related to P300 activity, and therefore study the activation timing. We found that the detection of rare targets, that is able to elicit the P300 component, stimulates a limbic-parieto-frontal circuit, with latencies ranging between 300 and 400 ms. Our findings suggest that the proposed approach might be extended to other event-related experimental paradigms, and might represent an valuable tool for a clearer understanding of the cerebral mechanisms underlying a wide range of cognitive functions. © 2007 IEEE.
124. Lotte, F., A. Lécuyer, and B. Arnaldi, FuRIA: A novel feature extraction algorithm for brain-computer interfaces using inverse models and fuzzy regions of interest. Proceedings of the 3rd International IEEE EMBS Conference on Neural Engineering, 2007: p. 175-178.
Summary: In this paper, we propose a new feature extraction algorithm for Brain-Computer Interfaces (BCIs). This algorithm is based on inverse models and uses the novel concept of fuzzy Region Of Interest (ROI). It can automatically identify the relevant ROIs and their reactive frequency bands. The activity in these ROIs can be used as features for any classifier. A first evaluation of the algorithm, using a Support Vector Machine (SVM) as classifier, is reported on data set IV from BCI competition 2003. Results are promising as we reached an accuracy on the test set ranging from 85% to 86% whereas the winner of the competition on this data set reached 84%. © 2007 IEEE.
125. Leal, A.J.R., S. Nunes, A.I. Dias, J.P. Vieira, A. Moreira, and E. Calado, Analysis of the generators of epileptic activity in early-onset childhood benign occipital lobe epilepsy. Clinical Neurophysiology, 2007. 118(6): p. 1341-1347.
Summary: Objective: The Panayiotopoulos type of idiopathic occipital epilepsy has peculiar and easily recognizable ictal symptoms, which are associated with complex and variable spike activity over the posterior scalp areas. These characteristics of spikes have prevented localization of the particular brain regions originating clinical manifestations. We studied spike activity in this epilepsy to determine their brain generators. Methods: The EEG of 5 patients (ages 7-9) was recorded, spikes were submitted to blind decomposition in independent components (ICs) and those to source analysis (sLORETA), revealing the spike generators. Coherence analysis evaluated the dynamics of the components. Results: Several ICs were recovered for posterior spikes in contrast to central spikes which originated a single one. Coherence analysis supports a model with epileptic activity originating near lateral occipital area and spreading to cortical temporal or parietal areas. Conclusions: Posterior spikes demonstrate rapid spread of epileptic activity to nearby lobes, starting in the lateral occipital area. In contrast, central spikes remain localized in the rolandic fissure. Significance: Rapid spread of posterior epileptic activity in the Panayitopoulos type of occipital lobe epilepsy is responsible for the variable and poorly localized spike EEG. The lateral occipital cortex is the primary generator of the epileptic activity. © 2007 International Federation of Clinical Neurophysiology.
126. Latif, M.A., S. Sanei, J. Chambers, and L. Spyrou, Partially Constrained Blind Source Separation for Localization of Unknown Sources Exploiting Non-homogeneity of the Head Tissues. Journal of VLSI Signal Processing Systems for Signal, Image, and Video Technology, 2007. 49(2): p. 217-232.
Summary: A new brain source localization technique using electroencephalograms (EEGs) is investigated in this paper. The information which describes the location of certain known sources is used as the constraint within the proposed blind source separation (BSS) algorithm and leads to a solution to the ill-posed inverse problem of source localization. Non-homogeneity of the head tissues, on the other hand, is exploited by introducing a realistic model of the mixing system. This model is used to better identify the location of the unknown sources within the brain from projection of the separated independent components on to the scalp. A separate procedure is employed to highlight the rhythmic EEG sources such as Alpha rhythm as the known sources. The performance of the scheme is shown on real EEG measurements and compared with that of "conventional dipole fitting algorithm". © 2007 Springer Science+Business Media, LLC.
127. Kopřivová, J., J. Praško, M. Brunovský, and J. Horáček, Independent component analysis of the EEG signal and its application in a patient with obsessive-compulsive disorder. Využití analýzy nezávislých komponent EEG signálu u nemocného s obsedantně-kompulzivní poruchou, 2007. 11(4): p. 240-243.
Summary: We demonstrate the potential diagnostic and therapeutic use of electrical brain activity information decomposed via independent component analysis (ICA) in an obsessive-compulsive patient. The resting EEG was analyzed by sLORETA (standardized low-resolution electromagnetic tomography) and by the ICA using the Independent Component Neurofeedback software (ICoN, Nova Tech EEG, Inc). The sLORETA normative database comparison (Nova Tech EEG, Inc) revealed increase of absolute power in the theta frequency band, especially in the anterior cingulate and orbitofrontal gyrus whose involvement in OCD pathophysiology has been previously reported. Abnormal theta waves were also detectable by visual EEG inspection. The ICA identified their main source, localized in the affective part of the anterior cingulate and in the medial orbitofrontal cortex. With respect to out findings we hypothesize that neurofeedback aimed at decreasing theta activity of this source might lead to the normalization of dysfunctional neural network and thus improve clinical symptoms.
128. Im, C.H., A. Gururajan, N. Zhang, W. Chen, and B. He, Spatial resolution of EEG cortical source imaging revealed by localization of retinotopic organization in human primary visual cortex. Journal of Neuroscience Methods, 2007. 161(1): p. 142-154.
Summary: The aim of the present study is to investigate the spatial resolution of electroencephalography (EEG) cortical source imaging by localizing the retinotopic organization in the human primary visual cortex (V1). Retinotopic characteristics in V1 obtained from functional magnetic resonance imaging (fMRI) study were used as reference to assess the spatial resolution of EEG since fMRI can discriminate small changes in activation in visual field. It is well known that the activation of the early C1 component in the visual evoked potential (VEP) elicited by pattern onset stimuli coincides well with the activation in the striate cortex localized by fMRI. In the present experiments, we moved small circular checkerboard stimuli along horizontal meridian and compared the activations localized by EEG cortical source imaging with those from fMRI. Both fMRI and EEG cortical source imaging identified spatially correlated activity within V1 in each subject studied. The mean location error, between the fMRI-determined activation centers in V1 and the EEG source imaging activation peak estimated at equivalent C1 components (peak latency: 74.8 ± 10.6 ms), was 7 mm (25% and 75% percentiles are 6.45 mm and 8.4 mm, respectively), which is less than the change in fMRI activation map by a 3° visual field change (7.8 mm). Moreover, the source estimates at the earliest major VEP component showed statistically good correlation with those obtained by fMRI. The present results suggest that the spatial resolution of the EEG cortical source imaging can correctly discriminate cortical activation changes in V1 corresponding to less than 3° visual field changes. © 2006 Elsevier B.V. All rights reserved.
129. Huber, R., S.K. Esser, F. Ferrarelli, M. Massimini, M.J. Peterson, and G. Tononi, TMS-induced cortical potentiation during wakefulness locally increases slow wave activity during sleep. PLoS ONE, 2007. 2(3).
Summary: Background. Sleep slow wave activity (SWA) is thought to reflect sleep need, increasing in proportion to the length of prior wakefulness and decreasing during sleep. However, the process responsible for SWA regulation is not known. We showed recently that SWA increases locally after a learning task involving a circumscribed brain region, suggesting that SWA may reflect plastic changes triggered by learning. Methodology/Principal Findings. To test this hypothesis directly, we used transcranial magnetic stimulation (TMS) in conjunction with high-density EEG in humans. We show that 5-Hz TMS applied to motor cortex induces a localized potentiation of TMS-evoked cortical EEG responses. We then show that, in the sleep episode following 5-Hz TMS, SWA increases markedly (+39.1±17.4%, p<0.01, n = 10). Electrode coregistration with magnetic resonance images localized the increase in SWA to the same premotor site as the maximum TMS-induced potentiation during wakefulness. Moreover, the magnitude of potentiation during wakefulness predicts the local increase in SWA during sleep. Conclusions/Significance. These results provide direct evidence for a link between plastic changes and the local regulation of sleep need. © 2007 Huber et al.
130. Hämäläinen, M.S., Progress and challenges in multimodal data fusion. International Congress Series, 2007. 1300: p. 15-18.
Summary: Independently, different brain imaging methods provide compromised spatial and temporal resolutions. Anatomical MRI provides highly accurate information about the individual cortical anatomy. In functional imaging, fMRI is temporally limited by the slow time course of the hemodynamic response, but can provide spatial sampling on a millimeter scale. EEG and MEG in turn provide a temporal resolution of milliseconds, but the localization of sources is more complicated because of the electromagnetic inverse problem. Combining information provided by both anatomical and functional MRI with EEG/MEG data thus facilitates the elucidation of the spatial distribution and temporal orchestration of human brain activity. © 2007.
131. Freunberger, R., W. Klimesch, M. Doppelmayr, and Y. Höller, Visual P2 component is related to theta phase-locking. Neuroscience Letters, 2007. 426(3): p. 181-186.
Summary: In this study we investigated the hypothesis whether P2-related differences tested in a visual priming paradigm are associated with theta phase-locking. We recorded the EEG from 31 electrodes and calculated phase-locking index and total power differences for frequencies between 2 and 20 Hz. ERPs (event-related potentials) were analyzed for P1, N1 and P2 components. P2 showed strongest task-related amplitude differences between congruent and incongruent targets. A source analyses was performed for the P2 component using sLoreta that revealed local generators of the P2 in parieto-occipital regions. Phase-locking analyses showed specific effects in the theta range (4-6 Hz) appearing in time windows at around the P2 component. We draw the conclusion that phase-locked theta reflect top-down regulation processes mediating information between memory systems and is in part involved in the modulation of the P2 component. © 2007 Elsevier Ireland Ltd. All rights reserved.
132. Du, Y., J.X. Zhang, Z. Xiao, and R. Wu, Neural systems and time course of proactive interference in working memory. Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings, 2007: p. 1136-1139.
Summary: The storage of information in working memory suffers as a function of proactive interference. Many works using neuroimaging technique have been done to reveal the brain mechanism of interference resolution. However, less is yet known about the time course of this process. Event-related potential method(ERP) and standardized Low Resolution Brain Electromagnetic Tomography method (sLORETA) were used in this study to discover the time course of interference resolution in working memory. The anterior P2 was thought to reflect interference resolution and if so, this process occurred earlier in working memory than in long-term memory. © 2007 IEEE.
133. Dongil, C., C. Sumin, L. Jaewon, K. Sungyo, K. Sangwoo, P. Hyunsang, R. Shinho, and J. Jaeseung, EEG source localization analysis for local-global visual processing using sLORETA. Proceedings of the 3rd International IEEE EMBS Conference on Neural Engineering, 2007: p. 568-571.
Summary: The aim of this study was to assess whether Standardized Low Resolution Brain Electromagnetic Tomography (sLORETA) can detect differences in EEG source distribution during local and global stimuli cognition process or not. We recorded the cortical brain activity from 40 subjects (M:F=20:20) during local and global stimuli cognition process. The stimuli were generated based on the modified version of Navon's hierarchical structured stimuli . We found the differences in 4-8 Hz theta oscillation during the task between male and female groups in sLORETA patterns, particularly in the right temporal cortex. We also found the similar theta oscillation patterns in power spectrum analysis: higher synchronized theta activity between posterior parietal lobe and frontal lobe was found in female group than that of male group. These findings suggest higher dependence on local-global stimulation cognition and memory recall in female. We suggest that sLORETA can be a good tool for detecting local-global stimulus cognition and be a good diagnostic for the neuropsychiatric disorders related to the local-global processing such as Obsessive-compulsive disorder and Posttraumatic stress disorder. © 2007 IEEE.
134. Ding, L. and B. He, Sparse source imaging in EEG. Proc. of 2007 Joint Meet. of the 6th Int. Symp. on Noninvasive Functional Source Imaging of the Brain and Heart and the Int. Conf. on Functional Biomedical Imaging, NFSI and ICFBI 2007, 2007: p. 20-23.
Summary: We have developed a new L1-norm based minimum norm estimate (MNE), which is termed as sparse source imaging (SSI). The new SSI algorithm corrects inaccurate orientation discrepancy in previously reported L1-norm MNEs. A new solver to the newly developed SSI has been adopted and known as the second order cone programming (SOCP). The new SSI is assessed by a series of computer simulations. The performance of SSI is compared with other L1-norm MNEs by evaluating the localization error and orientation error. The present simulation results indicate that the new SSI has significantly improved performance, especially in the metric of orientation error. The previously reported L1-norm MNEs show large orientation errors due to the orientation discrepancy. The new SSI algorithm is also applicable to MEG source imaging. © 2007 IEEE.
135. Dammers, J., H. Mohlberg, F. Boers, P. Tass, K. Amunts, and K. Mathiak, A new toolbox for combining magnetoencephalographic source analysis and cytoarchitectonic probabilistic data for anatomical classification of dynamic brain activity. NeuroImage, 2007. 34(4): p. 1577-1587.
Summary: Size and location of activated cortical areas are often identified in relation to their surrounding macro-anatomical landmarks such as gyri and sulci. The sulcal pattern, however, is highly variable. In addition, many cortical areas are not linked to well defined landmarks, which in turn do not have a fixed relationship to functional and cytoarchitectonic boundaries. Therefore, it is difficult to unambiguously attribute localized neuronal activity to the corresponding cortical areas in the living human brain. Here we present new methods that are implemented in a toolbox for the objective anatomical identification of neuromagnetic activity with respect to cortical areas. The toolbox enables the platform independent integration of many types of source analysis obtained from magnetoencephalography (MEG) together with probabilistic cytoarchitectonic maps obtained in postmortem brains. The probability maps provide information about the relative frequency of a given cortical area being located at a given position in the brain. In the new software, the neuromagnetic data are analyzed with respect to cytoarchitectonic maps that have been transformed to the individual subject brain space. A number of measures define the degree of overlap between and distance from the activated areas and the corresponding cytoarchitectonic maps. The implemented algorithms enable the investigator to quantify how much of the reconstructed current density can be attributed to distinct cortical areas. Dynamic correspondence patterns between the millisecond-resolved MEG data and the static cytoarchitectonic maps are obtained. We show examples for auditory and visual activation patterns. However, size and location of the postmortem brain areas as well as the inverse method applied to the neuromagnetic data bias the anatomical classification. Therefore, the adaptation to the respective application and a combination of the objective quantities are discussed. © 2006 Elsevier Inc. All rights reserved.
136. Cannon, R., J. Lubar, M. Congedo, K. Thornton, K. Towler, and T. Hutchens, The effects of neurofeedback training in the cognitive division of the anterior cingulate gyrus. International Journal of Neuroscience, 2007. 117(3): p. 337-357.
Summary: This study examines the efficacy of neurofeedback training in the cognitive division of the anterior cingulate gyrus and describes its relationship with cortical regions known to be involved in executive functions. This study was conducted with eight non-clinical students, four male and four female, with a mean age of twenty-two. Learning occurred in the ACcd at significant levels over sessions and in the anterior regions that receive projections from the AC. There appears to be a multidimensional executive circuit that increases in the same frequency in apparent synchrony with the AC and it may be possible to train this sub-cortical region using LNFB. Copyright © 2007 Informa Healthcare.
137. Belardinelli, P., L. Ciancetta, M. Staudt, V. Pizzella, A. Londei, N. Birbaumer, G.L. Romani, and C. Braun, Cerebro-muscular and cerebro-cerebral coherence in patients with pre- and perinatally acquired unilateral brain lesions. NeuroImage, 2007. 37(4): p. 1301-1314.
Summary: The cerebral networks involved in motor control were analyzed in four young hemi-paretic patients (21-25 years) with pre- and perinatally acquired brain lesions (3 with left periventricular brain lesions, 1 with left schizencephaly) by means of MEG source coherence analysis. Previous TMS and fMRI studies on the same patients had investigated their residual ability to move the paretic hand by means of a reorganized primary motor cortex (M1) representation in the contralesional hemisphere. The purpose of this study is to identify the effects of such a cerebral reorganization and the related dynamic aspects which allow the patients to move the paretic arm. Patients underwent a pinch grip task (1-N isometric contraction) using their paretic and non-paretic hands in alternation. MEG signals were recorded using a whole-head 151-channel magnetoencephalograph. EMG was simultaneously recorded as a reference for coherence calculations. 3D coherence mapping was performed in the β frequency range (14-30 Hz). This approach confirmed the relocation of motor functions from the lesioned (left) to the contralesional (right) hemisphere. In case of left, non-paretic pinch grip, coherent activity originated from contralateral (right) M1 exclusively. In the case of right (paretic) grip, coherent activity in ipsilateral M1 as well as significant coherence of ipsilateral cerebellum with both muscle activity and M1 itself was detected in 3 out of 4 subjects. As expected, the patient with no cerebellar involvement during paretic hand contraction showed the worst motor performance in the grip task. Coupling direction analysis demonstrated that throughout pinch grip the coupling direction goes from M1 to cerebellum. The present study verified the assumption that the intact hemisphere takes over motor control from the paretic (ipsilateral) hand in the presence of early unilateral brain lesion. Moreover, the role of cerebellum in motor deficit compensation and its close interaction with ipsilateral primary motor cortex was studied in detail. © 2007 Elsevier Inc. All rights reserved.
138. Belardinelli, P., L. Ciancetta, M. Staudt, V. Pizzella, A. Londei, N. Birbaumer, G.L. Romani, and C. Braun, From where to how: Assessing mechanisms of neural plasticity in patients with unilateral brain lesions. Proc. of 2007 Joint Meet. of the 6th Int. Symp. on Noninvasive Functional Source Imaging of the Brain and Heart and the Int. Conf. on Functional Biomedical Imaging, NFSI and ICFBI 2007, 2007: p. 362-364.
Summary: A set of different algorythms was involved to analyze the anomalous motor control in four young hemi-paretic patients with pre- and perinatally acquired brain lesions. The effects of a peculiar cerebral reorganization allow the patients to move the paretic arm. Patients performed a pinch grip using their paretic and non-paretic hands alternatively. EMG was simultaneously recorded as a basis for coherence calculations. 3D coherence mapping was performed in the β frequency range. Such approach evidenced the relocation of motor functions from the lesioned (left) to the contralesional (right) hemisphere. While in case of left, non-paretic pinch grip, coherent activity originated from contralateral (right) M1 exclusively, right (paretic) grip, produced coherent activity in ipsilateral M1 as well as significant coherence of ipsilateral cerebellum. Coupling direction analysis demonstrated that throughout pinch grip the coupling direction goes from M1 to cerebellum. © 2007 IEEE.
139. Banaschewski, T. and D. Brandeis, Annotation: What electrical brain activity tells us about brain function that other techniques cannot tell us - A child psychiatric perspective. Journal of Child Psychology and Psychiatry and Allied Disciplines, 2007. 48(5): p. 415-435.
Summary: Background: Monitoring brain processes in real time requires genuine subsecond resolution to follow the typical timing and frequency of neural events. Non-invasive recordings of electric (EEG/ERP) and magnetic (MEG) fields provide this time resolution. They directly measure neural activations associated with a wide variety of brain states and processes, even during sleep or in infants. Mapping and source estimation can localise these time-varying activation patterns inside the brain. Methods: Recent EEG/ERP research on brain functions in the domains of attention and executive functioning, perception, memory, language, emotion and motor processing in ADHD, autism, childhood-onset schizophrenia, Tourette syndrome, specific language disorder and developmental dyslexia, anxiety, obsessive-compulsive disorder, and depression is reviewed. Results: Over the past two decades, electrophysiology has substantially contributed to the understanding of brain functions during normal development, and psychiatric conditions of children and adolescents. Its time resolution has been important to measure covert processes, and to distinguish cause and effect. Conclusion: In the future, EEG/ERP parameters will increasingly characterise the interplay of neural states and information processing. They are particularly promising tools for multilevel investigations of etiological pathways and potential predictors of clinical treatment response. © 2007 The Authors Journal compilation © 2007 Association for Child and Adolescent Mental Health.
140. Bai, X., V.L. Towle, E.J. He, and B. He, Evaluation of cortical current density imaging methods using intracranial electrocorticograms and functional MRI. NeuroImage, 2007. 35(2): p. 598-608.
Summary: Objective: EEG source imaging provides important information regarding the underlying neural activity from noninvasive electrophysiological measurements. The aim of the present study was to evaluate source reconstruction techniques by means of the intracranial electrocorticograms (ECoGs) and functional MRI. Methods: Five source imaging algorithms, including the minimum norm least square (MNLS), LORETA with Lp-norm (p equal to 1, 1.5 and 2), sLORETA, the minimum Lp-norm (p equal to 1 and 1.5; when p = 2, the MNLS method is mathematically equivalent to the minimum Lp-norm) and L1-norm (the linear programming) methods, were evaluated in a group of 10 human subjects, in a paradigm with somatosensory stimulation. Cortical current density (CCD) distributions were estimated from the scalp somatosensory evoked potentials (SEPs), at approximately 30 ms following electrical stimulation of median nerve at the wrist. Realistic geometry boundary element head models were constructed from the MRIs of each subject and used in the CCD analysis. Functional MRI results obtained from a motor task and sensory stimulation in all subjects were used to identify the central sulcus, motor and sensory areas. In three patients undergoing neurosurgical evaluation, ECoGs were recorded in response to the somatosensory stimulation, and were used to help determine the central sulcus and the sensory cortex. Results: The CCD distributions estimated by the Lp-norm and LORETA-Lp methods were smoother when the p values were high. The LORETA based on the L1-norm performed better than the LORETA-L2 method for imaging well localized sources such as the P30 component of the SEP. The mean and standard deviation of the distance between the location of maximum CCD value and the central sulcus, estimated by the minimum Lp-norm (with p equal to 1), L1-norm (the Linear programming) and LORETA-Lp (with p equal to 1) methods, were 4, 7, 7 mm and 3, 4, 2 mm, respectively (after converting into Talairach coordinates). The mean and standard deviation of the aforementioned distance, estimated by the MNLS, LORETA with Lp-norm (p equal to 1.5 and 2.0), sLORETA and the minimum Lp-norm (p equal to 1.5) methods, were over 11 mm and 6 mm, respectively. Conclusions: The present experimental study suggests that L1-norm-based algorithms provide better performance than L2 and L1.5-norm-based algorithms, in the context of CCD imaging of well localized sources induced by somatosensory electrical stimulation of median nerve at the wrist. © 2006 Elsevier Inc. All rights reserved.
141. Alain, C., J.S. Snyder, Y. He, and K.S. Reinke, Changes in auditory cortex parallel rapid perceptual learning. Cerebral Cortex, 2007. 17(5): p. 1074-1084.
Summary: Learning perceptual skills is characterized by rapid improvements in performance within the first hour of training (fast perceptual learning) followed by more gradual improvements that take place over several daily practice sessions (slow perceptual learning). Although it is widely accepted that slow perceptual learning is accompanied by enhanced stimulus representation in sensory cortices, there is considerable controversy about the neural substrates underlying early and rapid improvements in learning perceptual skills. Here we measured event-related brain potentials while listeners were presented with 2 phonetically different vowels. Listeners' ability to identify both vowels improved gradually during the first hour of testing and was paralleled by enhancements in an early evoked response (∼130 ms) localized in the right auditory cortex and a late evoked response (∼340 ms) localized in the right anterior superior temporal gyrus and/or inferior prefrontal cortex. These neuroplastic changes depended on listeners' attention and were preserved only if practice was continued; familiarity with the task structure (procedural learning) was not sufficient. We propose that the early increases in cortical responsiveness reflect goal-directed changes in the tuning properties of auditory neurons involved in parsing concurrent speech signals. Importantly, the neuroplastic changes occurred rapidly, demonstrating the flexibility of human speech segregation mechanisms. © The Author 2006. Published by Oxford University Press. All rights reserved.
142. Rodríguez-Rivera, A., B.V. Baryshnikov, B.D. Van Veen, and R.T. Wakai, MEG and EEG source localization in beamspace. IEEE Transactions on Biomedical Engineering, 2006. 53(3): p. 430-441.
Summary: Beamspace methods are applied to EEG/MEG source localization problems in this paper. Beamspace processing involves passing the data through a linear transformation that reduces the data dimension prior to applying a desired statistical signal processing algorithm. This process generally reduces the data requirements of the subsequent algorithm. We present one approach for designing beamspace transformations that are optimized to preserve source activity located within a given region of interest and show that substantial reductions in dimension are obtained with negligible signal loss. Beamspace versions of maximum likelihood dipole fitting, MUSIC, and minimum variance beamforming source localization algorithms are presented. The performance improvement offered by the beamspace approach with limited data is demonstrated by bootstrapping somatosensory data to evaluate the variability of the source location estimates obtained with each algorithm. The quantitative benefits of beamspace processing depend on the algorithm, signal to noise ratio, and amount of data. Dramatic performance improvements are obtained in scenarios with low signal to noise ratio and a small number of independent data samples. © 2006 IEEE.
143. Nakamura, W., S. Koyama, S. Kuriki, and Y. Inouye, Estimation of current density distributions from EEG/MEG data by maximizing sparseness of spatial difference. Proceedings - IEEE International Symposium on Circuits and Systems, 2006: p. 1071-1074.
Summary: Separation of EEG(Electroencephalography) or MEG(Magnetoencephalography) data into activations of small dipoles or current density distribution is an ill-posed problem in which the number of parameters to estimate is larger than the dimension of the data. Several constraints have been proposed and used to avoid this problem, such as minimization of the Linorm of the current distribution or minimization of Laplacian of the distribution. In this paper, we propose another constraint that the current density distribution changes at only a small number of areas and these changes can be large. By numerical experiments, we show that the proposed method estimates current distribution well from both data generated by strongly localized current distributions and data generated by currents broadly distributed. © 2006 IEEE.
144. Liu, H. and P.H. Schimpf, Efficient localization of synchronous EEG source activities using a modified RAP-MUSIC algorithm. IEEE Transactions on Biomedical Engineering, 2006. 53(4): p. 652-661.
Summary: Synchronization across different brain regions is suggested to be a possible mechanism for functional integration. Noninvasive analysis of the synchronization among cortical areas is possible if the electrical sources can be estimated by solving the electroencephalography inverse problem. Among various inverse algorithms, spatio-temporal dipole fitting methods such as RAP-MUSIC and R-MUSIC have demonstrated superior ability in the localization of a restricted number of independent sources, and also have the ability to reliably reproduce temporal waveforms. However, these algorithms experience difficulty in reconstructing multiple correlated sources. Accurate reconstruction of correlated brain activities is critical in synchronization analysis. In this study, we modified the well-known inverse algorithm RAP-MUSIC to a multistage process which analyzes the correlation of candidate sources and searches for independent topographies (ITs) among precorrelated groups. Comparative studies were carried out on both simulated data and clinical seizure data. The results demonstrated superior performance with the modified algorithm compared to the original RAP-MUSIC in recovering synchronous sources and localizing the epileptiform activity. The modified RAP-MUSIC algorithm, thus, has potential in neurological applications involving significant synchronous brain activities. © 2006 IEEE.
145. Lin, F.H., T. Witzel, S.P. Ahlfors, S.M. Stufflebeam, J.W. Belliveau, and M.S. Hämäläinen, Assessing and improving the spatial accuracy in MEG source localization by depth-weighted minimum-norm estimates. NeuroImage, 2006. 31(1): p. 160-171.
Summary: Cerebral currents responsible for the extra-cranially recorded magnetoencephalography (MEG) data can be estimated by applying a suitable source model. A popular choice is the distributed minimum-norm estimate (MNE) which minimizes the ℓ2-norm of the estimated current. Under the ℓ2-norm constraint, the current estimate is related to the measurements by a linear inverse operator. However, the MNE has a bias towards superficial sources, which can be reduced by applying depth weighting. We studied the effect of depth weighting in MNE using a shift metric. We assessed the localization performance of the depth-weighted MNE as well as depth-weighted noise-normalized MNE solutions under different cortical orientation constraints, source space densities, and signal-to-noise ratios (SNRs) in multiple subjects. We found that MNE with depth weighting parameter between 0.6 and 0.8 showed improved localization accuracy, reducing the mean displacement error from 12 mm to 7 mm. The noise-normalized MNE was insensitive to depth weighting. A similar investigation of EEG data indicated that depth weighting parameter between 2.0 and 5.0 resulted in an improved localization accuracy. The application of depth weighting to auditory and somatosensory experimental data illustrated the beneficial effect of depth weighting on the accuracy of spatiotemporal mapping of neuronal sources. © 2005 Elsevier Inc. All rights reserved.
146. Larson-Prior, L.J., J. Zempel, and A.Z. Snyder, Imaging across scale: The promise of multi-modal imaging. 2006 IEEE/NLM Life Science Systems and Applications Workshop, LiSA 2006, 2006.
Summary: Comprehending neural function requires techniques that permit measurement of large-scale activity over complex networks even as we gain greater understanding of the foundations of this activity at the level of single or small populations of neurons. The measurement techniques currently available, while having yielded important and relevant information on the complexity of global neural networks, still provide only snapshots of the full picture. At present, recording and analysis remain linked to the spatial or temporal resolution inherent to each technique. Thus, the ability to integrate electrophysiological and functional imaging techniques to gain access to the spatio-temporal dynamics of neural activity is an important frontier in modern imaging science. © 2006 IEEE.
147. Küçükaltun-Yildirim, E., D. Pantazis, and R.M. Leahy, Task-based comparison of inverse methods in magnetoencephalography. IEEE Transactions on Biomedical Engineering, 2006. 53(9): p. 1783-1793.
Summary: Magnetoencephalography (MEG) provides unique insights into the spatio-temporal dynamics of neural activation in the human brain. Unfortunately, the accuracy with which neural sources can be localized is limited by the highly illposed nature of the inverse problem. A large number of inverse methods have been proposed that deal with this illposedness using a range of different modeling and regularization procedures. Here we describe an objective task-based framework for comparing different inverse methods. Using the free-response receiver operating characteristic (FROC) we compare the performance of matched filters, cortically constrained dipole scanning, and minimum norm imaging methods for the task of detecting focal cortical activation. Our results indicate that the scanning methods outperform matched filters and minimum norm imaging for the case of one and two 2 cm2 patches of cortical activity when the dynamics of the two patches are both strongly and weakly correlated and irrespective of the spacing of the two activated regions. © 2006 IEEE.
148. Kristeva, R., V. Chakarov, M. Wagner, J. Schulte-Mönting, and M.C. Hepp-Reymond, Is the movement-evoked potential mandatory for movement execution? A high-resolution EEG study in a deafferented patient. NeuroImage, 2006. 31(2): p. 677-685.
Summary: During simple self-paced index finger flexion with and without visual feedback of the finger, we compared the movement-evoked potentials of the completely deafferented patient GL with those of 7 age-matched healthy subjects. EEG was recorded from 58 scalp positions, together with the electromyogram (EMG) from the first dorsal interosseous muscle and the movement trace. We analyzed the movement parameters and the contralateral movement-evoked potential and its source. The patient performed the voluntary movements almost as well as the controls in spite of her lack of sensory information from the periphery. In contrast, the movement-evoked potential was observed only in the controls and not in the patient. These findings clearly demonstrate that the movement-evoked potential reflects cutaneous and proprioceptive feedback from the moving part of the body. They also indicate that in absence of sensory peripheral input the motor control switches from an internal "sensory feedback-driven" to a "feedforward" mode. The role of the sensory feedback in updating the internal models and of the movement-evoked potential as a possible cortical correlate of motor awareness is discussed. © 2006 Elsevier Inc. All rights reserved.
149. Kopeček, M., M. Brunovský, T. Novák, B. Tišlerová, J. Horáček, and C. Höschl, The effect of cerebellar repetitive transcranial magnetic stimulation on electrical brain activity detected by low resolution electromagnetic tomography. Psychiatrie, 2006. 10(SUPPL. 3): p. 54-58.
Summary: Background: Previous studies have detected EEG, cognitive and motor cortex modulation after cerebellar repetitive Transcranial Magnetic Stimulation (rTMS). The aim of our study was to determine a) if these findings actually reflect cerebellar rTMS or rather neck muscle magnetic stimulation (MMS), and b) if cerebellar rTMS modulates frontal cortex activity. Methods: EEG recordings were obtained from 6 right-handed healthy volunteers before and after 1) rTMS applied over the right cerebellar hemisphere and 2) MMS applied over the right muscle trapezius. We used 20 minutes of 10 Hz rTMS and MMS with 1200 impulses. The spatial distribution of the rTMS and MMS-induced changes in the electrical brain activity were assessed using low-resolution electromagnetic tomography (LORETA). Results: Right cerebellar rTMS increased the power density in the delta, theta, alpha-1 and beta-2 frequency bands. Power increments in the delta, theta and beta-2 bands were found predominantly over the frontal and parietal lobes, whereas the alpha-1 power was increased bilaterally in the medial cingulate. No significant changes were detected after MMS applied over the trapezius muscle. Conclusions: Our results suggest the feasibility to modulate frontal cortical activity by means of cerebellar rTMS. This could support the use of the cerebellar rTMS in patients with neuropsychiatric disorders where cortico-subcortico-cerebellar abnormalities have been detected.
150. Junghöfer, M., P. Peyk, T. Flaisch, and H.T. Schupp, Chapter 7 Neuroimaging methods in affective neuroscience: Selected methodological issues. Progress in Brain Research, 2006. 156: p. 123-143.
Summary: A current goal of affective neuroscience is to reveal the relationship between emotion and dynamic brain activity in specific neural circuits. In humans, noninvasive neuroimaging measures are of primary interest in this endeavor. However, methodological issues, unique to each neuroimaging method, have important implications for the design of studies, interpretation of findings, and comparison across studies. With regard to event-related brain potentials, we discuss the need for dense sensor arrays to achieve reference-independent characterization of field potentials and improved estimate of cortical brain sources. Furthermore, limitations and caveats regarding sparse sensor sampling are discussed. With regard to event-related magnetic field (ERF) recordings, we outline a method to achieve magnetoencephalography (MEG) sensor standardization, which improves effects' sizes in typical neuroscientific investigations, avoids the finding of ghost effects, and facilitates comparison of MEG waveforms across studies. Focusing on functional magnetic resonance imaging (fMRI), we question the unjustified application of proportional global signal scaling in emotion research, which can greatly distort statistical findings in key structures implicated in emotional processing and possibly contributing to conflicting results in affective neuroscience fMRI studies, in particular with respect to limbic and paralimbic structures. Finally, a distributed EEG/MEG source analysis with statistical parametric mapping is outlined providing a common software platform for hemodynamic and electromagnetic neuroimaging measures. Taken together, to achieve consistent and replicable patterns of the relationship between emotion and neuroimaging measures, methodological aspects associated with the various neuroimaging techniques may be of similar importance as the definition of emotional cues and task context used to study emotion. © 2006 Elsevier B.V. All rights reserved.
151. Jäncke, L., K. Lutz, and S. Koeneke, Chapter 18 Converging evidence of ERD/ERS and BOLD responses in motor control research. Progress in Brain Research, 2006. 159: p. 261-271.
Summary: In this chapter we summarize findings of our group in which we studied the neural underpinnings of finger tapping control using different methods (functional magnetic resonance imaging: fMRI, electroencephalography: EEG, transcranial magnetic stimulation: TMS, and behavioural experiments). First, we found that maximum finger tapping speed is a matter of training as shown for professional musicians. Secondly, we demonstrated that different finger tapping speeds are accompanied by different hemodynamic responses in the primary hand motor area (M1), the cerebellum and partly in pre-motor areas. With increasing tapping speed there is an increase of hemodynamic response in these areas (rate effect). Thirdly, the effect measured with fMRI is substantiated by rate effects measured by means of task-related power decreases in the upper α-band (10-12 Hz) over the primary motor cortex. In case of sequential finger movement learning, we observed decreases in task-related α-power in lateral PMC (event-related desynchronization: ERD) and simultaneous α-power increases in SMA (event-related synchronization: ERS) that came along with training-induced increases in movement rate. This pattern is discussed in relation to the "focal ERD/surround ERS" phenomenon suggested by Pfurtscheller and Lopes da Silva. Finally, we demonstrated that finger tapping speed was slowed by selectively inhibiting the primary hand motor area using TMS. Taken together, these studies demonstrate on the basis of converging evidence that the primary hand motor area is the basic control centre for controlling the movement parameter tapping speed. However, the neural efficiency to control finger tapping speed (as measured with hemodynamic responses or ERD/ERS patterns) is a matter of training. © 2006 Elsevier B.V. All rights reserved.
152. Huber, R., M.F. Ghilardi, M. Massimini, F. Ferrarelli, B.A. Riedner, M.J. Peterson, and G. Tononi, Arm immobilization causes cortical plastic changes and locally decreases sleep slow wave activity. Nature Neuroscience, 2006. 9(9): p. 1169-1176.
Summary: Sleep slow wave activity (SWA) is thought to reflect sleep need, increasing after wakefulness and decreasing after sleep. We showed recently that a learning task involving a circumscribed brain region produces a local increase in sleep SWA. We hypothesized that increases in cortical SWA reflect synaptic potentiation triggered by learning. To further investigate the link between synaptic plasticity and sleep, we asked whether a procedure leading to synaptic depression would cause instead a decrease in sleep SWA. We show here that if a subject's arm is immobilized during the day, motor performance deteriorates and both somatosensory and motor evoked potentials decrease over contralateral sensorimotor cortex, indicative of local synaptic depression. Notably, during subsequent sleep, SWA over the same cortical area is markedly reduced. Thus, cortical plasticity is linked to local sleep regulation without learning in the classical sense. Moreover, when synaptic strength is reduced, local sleep need is also reduced. © 2006 Nature Publishing Group.
153. Halder, P., A. Curt, S. Brem, A. Lang-Dullenkopf, K. Bucher, S. Kollias, and D. Brandeis, Preserved aspects of cortical foot control in paraplegia. NeuroImage, 2006. 31(2): p. 692-698.
Summary: While several recent imaging studies confirm that motor foot areas can still be activated in complete and chronic paraplegia, it remains unclear whether their functionality is also maintained or declines after years of "non-use". Force control is one of the most important and best investigated functions within the motor cortex. It has been repeatedly reported that the motor cortex is more active when higher forces have to be applied. We thus addressed the question of preserved cortical functions by comparing motor force control patterns in the event-related potentials of 10 motor complete paraplegic subjects and 10 controls after attempted (paraplegic patients)/executed (healthy controls) ballistic foot movements with three different force levels. In addition to the peak amplitudes reflecting force levels, peak latencies were also investigated to elucidate timing as another functional aspect of motor control. No significant group difference was found for the peak latencies, indicating that the timing of motor cortical activation is preserved. Concerning amplitudes, we found preserved cortical modulation of higher forces but distorted low force modulation, especially early after injury. These findings thus suggest that important aspects of cortical control over paralyzed limbs are maintained despite years of "non-use". © 2005 Elsevier Inc. All rights reserved.
154. Guo, C., L. Duan, W. Li, and K.A. Paller, Distinguishing source memory and item memory: Brain potentials at encoding and retrieval. Brain Research, 2006. 1118(1): p. 142-154.
Summary: Vivid memory for an episode generally includes memory for a central object or event plus memory for background context or source information. To assess neural differences between source and item memory, we used event-related potentials (ERPs) to monitor relevant memory processes at both encoding and retrieval. Participants fluent in Chinese studied Chinese words superimposed on a square or circular background during the study phase, followed by a 1-min delay. Then, memory was tested for both the words (items) and the corresponding background (source), or, in other blocks, tested for the words alone. ERPs to study-phase words differed as a function of whether the word was later remembered. These Dm effects in the interval from 400 to 600 ms, however, did not differ according to whether or not source was remembered. In contrast, ERPs to test-phase words showed clear old/new effects that did differ across conditions. When both item and source were remembered accurately, old/new effects emerged earlier and were larger in amplitude than when source memory was either incorrect or not queried. These results demonstrate that encoding processes indexed by ERPs may have primarily reflected encoding of the visual and semantic properties of these words, stressing item memory over source memory. Retrieval processes indexed by ERPs, in contrast, likely reflected a combination of item retrieval, source retrieval, and related processing engaged when people were remembering words seen earlier. © 2006 Elsevier B.V. All rights reserved.
155. Grova, C., J. Daunizeau, J.M. Lina, C.G. Bénar, H. Benali, and J. Gotman, Evaluation of EEG localization methods using realistic simulations of interictal spikes. NeuroImage, 2006. 29(3): p. 734-753.
Summary: Performing an accurate localization of sources of interictal spikes from EEG scalp measurements is of particular interest during the presurgical investigation of epilepsy. The purpose of this paper is to study the ability of six distributed source localization methods to recover extended sources of activated cortex. Due to the frequent lack of a gold standard to evaluate source localization methods, our evaluation was performed in a controlled environment using realistic simulations of EEG interictal spikes, involving several anatomical locations with several spatial extents. Simulated data were corrupted by physiological EEG noise. Simulations involving pairs of sources with the same amplitude were also studied. In addition to standard validation criteria (e.g., geodesic distance or mean square error), we proposed an original criterion dedicated to assess detection accuracy, based on receiver operating characteristic (ROC) analysis. Six source localization methods were evaluated: the minimum norm, the minimum norm weighted by multivariate source prelocalization (MSP), cortical LORETA with or without additional minimum norm regularization, and two derivations of the maximum entropy on the mean (MEM) approach. Results showed that LORETA-based and MEM-based methods were able to accurately recover sources of different spatial extents, with the exception of sources in temporo-mesial and fronto-mesial regions. Several spurious sources were generated by those methods, however, whereas methods using the MSP always located very accurately the maximum of activity but not its spatial extent. These findings suggest that one should always take into account the results from different localization methods when analyzing real interictal spikes. © 2005 Elsevier Inc. All rights reserved.
156. Galderisi, S. and W.G. Sannita, Pharmaco-EEG: A history of progress and a missed opportunity. Clinical EEG and Neuroscience, 2006. 37(2): p. 61-65.
157. Finnigan, S.P., S.E. Rose, and J.B. Chalk, Rapid EEG changes indicate reperfusion after tissue plasminogen activator injection in acute ischaemic stroke. Clinical Neurophysiology, 2006. 117(10): p. 2338-2339.
158. Dong, G., R. Bayford, H. Liu, Y. Zhou, and W. Yan, EIT images with improved spatial resolution using a realistic head model. Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings, 2006: p. 1134-1137.
Summary: A recursive algorithm is presented to improve the spatial resolution of 3-D Electrical Impedance Tomography (EIT) images in a four-shell realistic head model. In this algorithm, the low spatial resolution image derived from the standardized Low resolution electromagnetic tomography algorithm (sLORETA) is chosen to be the initial estimate for the Focal Underdetermined System Solver (FOCUSS), and a shrinking strategy is adopted for adjusting the source space during iteration process in FOCUSS. Images are presented with improved spatial resolution and the algorithm effectiveness is verified on simulated data by setting two perturbations in the movement and visual regions of the brain. © 2006 IEEE.
159. Deouell, L.Y., A. Parnes, N. Pickard, and R.T. Knight, Spatial location is accurately tracked by human auditory sensory memory: Evidence from the mismatch negativity. European Journal of Neuroscience, 2006. 24(5): p. 1488-1494.
Summary: The nature of spatial representation in human auditory cortex remains elusive. In particular, although humans can discriminate the locations of sounds as close as 1-10 degrees apart, such resolution has not been shown in auditory cortex of humans or animals. We used the mismatch negativity (MMN) event related brain potential to measure the neural response to spatial change in humans in narrow 10 degree spatial steps. Twelve participants were tested using a dense array EEG setup while watching a silent movie and ignoring the sounds. The MMN was reliably elicited by infrequent changes of spatial location of sounds in free field. The MMN amplitude was linearly related to the degree of spatial change with a resolution of at least 10 degrees. These electrophysiological responses occurred within a window of 100-200 milliseconds from stimulus onset, and were localized to the posterior superior temporal gyrus. We conclude that azimuthal spatial displacement is rapidly, accurately and automatically represented in auditory sensory memory in humans, at the level of the auditory cortex. © The Authors (2006).
160. Daunizeau, J., J. Mattout, D. Clonda, B. Goulard, H. Benali, and J.M. Lina, Bayesian spatio-temporal approach for EEG source reconstruction: Conciliating ECD and distributed models. IEEE Transactions on Biomedical Engineering, 2006. 53(3): p. 503-516.
Summary: Characterizing the cortical activity sources of electroencephalography (EEG)/magnetoencephalography data is a critical issue since it requires solving an ill-posed inverse problem that does not admit a unique solution. Two main different and complementary source models have emerged: equivalent current dipoles (ECD) and distributed linear (DL) models. While ECD models remain highly popular since they provide an easy way to interpret the solutions, DL models (also referred to as imaging techniques) are known to be more realistic and flexible. In this paper, we show how those two representations of the brain electromagnetic activity can be cast into a common general framework yielding an optimal description and estimation of the EEG sources. From this extended source mixing modelw we derive a hybrid approach whose key aspect is the separation between temporal and spatial characteristics of brain activity, which allows to dramatically reduce the number of DL model parameters. Furthermore, the spatial profile of the sources, as a temporal invariant map, is estimated using the entire time window data, allowing to significantly enhance the information available about the spatial aspect of the EEG inverse problem. A Bayesian framework is introduced to incorporate distinct temporal and spatial constraints on the solution and to estimate both parameters and hyperparameters of the model. Using simulated EEG data, the proposed inverse approach is evaluated and compared with standard distributed methods using both classical criteria and ROC curves. © 2006 IEEE.
161. Congedo, M., F. Lotte, and A. Lécuyer, Classification of movement intention by spatially filtered electromagnetic inverse solutions. Physics in Medicine and Biology, 2006. 51(8): p. 1971-1989.
Summary: We couple standardized low-resolution electromagnetic tomography, an inverse solution for electroencephalography (EEG) and the common spatial pattern, which is here conceived as a data-driven beamformer, to classify the benchmark BCI (brain-computer interface) competition 2003, data set IV. The data set is from an experiment where a subject performed a self-paced left and right finger tapping task. Available for analysis are 314 training trials whereas 100 unlabelled test trials have to be classified. The EEG data from 28 electrodes comprise the recording of the 500 ms before the actual finger movements, hence represent uniquely the left and right finger movement intention. Despite our use of an untrained classifier, and our extraction of only one attribute per class, our method yields accuracy similar to the winners of the competition for this data set. The distinct advantages of the approach presented here are the use of an untrained classifier and the processing speed, which make the method suitable for actual BCI applications. The proposed method is favourable over existing classification methods based on an EEG inverse solution, which rely either on iterative algorithms for single-trial independent component analysis or on trained classifiers. © 2006 IOP Publishing Ltd.
162. Congedo, M., Subspace projection filters for real-time brain electromagnetic imaging. IEEE Transactions on Biomedical Engineering, 2006. 53(8): p. 1624-1634.
Summary: An increasing number of neuroimaging laboratories are becoming interested in real-time investigations of the human brain. The opportunities offered by real-time applications are inversely proportional to the latency of the brain activity response and to the computational delay of brain activity estimation. Electromagnetic tomographies, based on electroencephalography (EEG) or magnetoencephalography (MEG), feature immediacy of brain activity response and excellent time resolution, hence they are natural candidates. However their spatial resolution and signal-to-noise ratio are poor. In this paper, we develop data-independent and data-dependent subspace projection filters for the standardized low-resolution electromagnetic tomography (sLORETA), a weighted minimum norm inverse solution for EEG/MEG. The filters are designed for extracting time-series of source activity in any given region of interest. The data-independent filter is shown to reduce interference of sources originating in neighboring regions, whereas the data-dependent filter is shown to suppress sensor measurement noise. An effective and straightforward way to combine them is demonstrated. The result is a dual subspace projection allowing both noise suppression and interference reduction. © 2006 IEEE.
163. Browne, R.O., L.B. Moyal-Segal, D. Zumsteg, Y. David, O. Kofman, A. Berger, H. Soreq, and A. Friedman, Coding region paraoxonase polymorphisms dictate accentuated neuronal reactions in chronic, sub-threshold pesticide exposure. FASEB Journal, 2006. 20(10).
Summary: Organophosphate pesticides (OPs), known inhibitors of acetylcholinesterase (AChE), are used extensively throughout the world. Recent studies have focused on the ACHE/PON1 locus as a determinant of inherited susceptibility to environmental OP exposure. To explore the relationship of the corresponding gene-environment interactions with brain activity, we integrated neurophysiologic, neuropsychological, biochemical, and genetic methods. Importantly, we found that subthreshold OP exposure leads to discernible physiological consequences that are significantly influenced by inherited factors. Cortical EEG analyses by LORETA revealed significantly decreased theta activity in the hippocampus, parahippocampal regions, and the cingulate cortex, as well as increased beta activity in the prefrontal cortex of exposed individuals - areas known to play a role in cholinergic-associated cognitive functions. Through neuropsychological testing, we identified an appreciable deficit in the visual recall in exposed individuals. Other neuropsychological tests revealed no significant differences between exposed and non-exposed individuals, attesting to the specificity of our findings. Biochemical analyses of blood samples revealed increases in paraoxonase and arylesterase activities and reduced serum acetylcholinesterase activity in chronically exposed individuals. Notably, specific paraoxonase genotypes were found to be associated with these exposure-related changes in blood enzyme activities and abnormal EEG patterns. Thus, gene-environment interactions involving the ACHE/PON1 locus may be causally involved in determining the physiological response to OP exposure. © FASEB.
164. Belardinelli, P., L. Ciancetta, V. Pizzella, C. Del Gratta, and G.L. Romani, Localizing complex neural circuits with MEG data. Cognitive Processing, 2006. 7(1): p. 53-59.
Summary: During cognitive processing, the various cortical areas, with specialized functions, supply for different tasks. In most cases then, the information flows are processed in a parallel way by brain networks which work together integrating the single performances for a common goal. Such a step is generally performed at higher processing levels in the associative areas. The frequency range at which neuronal pools oscillate is generally wider than the one which is detectable by bold changes in fMRI studies. A high time resolution technique like magnetoencephalography or electroencephalography is therefore required as well as new data processing algorithms for detecting different coherent brain areas cooperating for one cognitive task. Our experiments show that no algorithm for the inverse problem solution is immune from bias. We propose therefore, as a possible solution, our software LOCANTO (Localization and Coherence ANalysis TOol). This new package features a set of tools for the detection of coherent areas. For such a task, as a default, it employs the algorithm with best performances for the neural landscape to be detected. If the neural landscape under attention involves more than two interacting areas the SLoreta algorithm is used. Our study shows in fact that SLoreta performance is not biased when the correlation among multiple sources is high. On the other hand, the Beamforming algorithm is more precise than SLoreta at localizing single or double sources but it gets a relevant localization bias when the sources are more than three and are highly correlated. © Marta Olivetti Belardinelli and Springer-Verlag 2006.
165. Bai, X., V.L. Towle, E.J. He, and B. He, Evaluation of cortical imaging techniques based on somatosensory evoked potentials. Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings, 2006: p. 1000-1001.
Summary: In the present study we evaluate the performance of several inverse algorithms for reconstructing the cortical current density distributions from scalp EEG recordings. The direct cortical SEP recordings In a patient were used as a gold standard to assess the performance of the numerical algorithms. The present results suggest that L1-norm methods gave the most accurate results in terms of cortical current density Imaging of brain responses invoked by somatosensory stimulation. © 2006 IEEE.
166. An, K.O., C.H. Im, C. Lee, H.K. Jung, and K.Y. Jung, Improved magnetoencephalography source reconstruction considering anatomical connectivity of cortical sources. IEEE Transactions on Magnetics, 2006. 42(4): p. 1379-1382.
Summary: In this paper, an improved magnetoencephalography (MEG) source reconstruction technique considering anatomical connectivity of cortical sources is proposed. The anatomical connectivity information was taken into account by calculating three-dimensional geodesic distance between neighboring sources, and then the resultant inverse solutions were compared with those of other cases: 1) inverse estimate without connectivity information; 2) use of Euclidean distance instead of geodesic distance. The proposed technique was applied to realistic simulations for a real brain anatomy, and the results showed that estimated sources can be smoother and more accurate by using the anatomical connectivity information. © 2006 IEEE.
167. Wu, W., W. Jia, H. Liu, X. Gao, G. Zhang, and Y. Wang, Localization of epileptic foci from preictal EEG data using standardized shrinking Loreta-Focuss algorithm. 2005 First International Conference on Neural Interface and Control, Proceedings, 2005: p. 209-212.
Summary: To localize epileptic foci, EEG source localization methods are often applied to interictal or ictal EEG data. However, ictal epileptiform is often interfered with artifacts caused by the movement of the patient. In this paper we use an algorithm called Standardized Shrinking LORETA-FOCUSS (SSLOFO) with a three-shell head model to reconstruct the sources from the EEC data of an epileptic patient during four subperiods, with three preictal and one ictal. The results demonstrate that using preictal EEG SSLOFO can accurately localize the epileptic foci in the left frontal lobe, as has been confirmed by intracranial recordings. The present study also suggests that we may use the trends of the estimated source energy with time to predict epileptic seizures. © 2005 IEEE.
168. Weber, D.L., C.R. Clark, A.C. McFarlane, K.A. Moores, P. Morris, and G.F. Egan, Abnormal frontal and parietal activity during working memory updating in post-traumatic stress disorder. Psychiatry Research - Neuroimaging, 2005. 140(1): p. 27-44.
Summary: This study used event-related potentials (ERPs) to investigate the timing and scalp topography of working memory in post-traumatic stress disorder (PTSD). This study was designed to investigate ERPs associated with a specific working memory updating process. ERPs were recorded from 10 patients and 10 controls during two visual tasks where (a) targets were a specific word or (b) targets were consecutive matching words. In the first task, nontarget words are not retained in working memory. In the second task, as in delay-match-to-sample tasks, a non-target word defines a new target identity, so these words are retained in working memory. This working memory updating process was related to large positive ERPs over frontal and parietal areas at 400-800 ms, which were smaller in PTSD. Estimation of cortical source activity indicated abnormal patterns of frontal and parietal activity in PTSD, which were also observed in regional cerebral blood flow [Clark, C.R., McFarlane, A.C., Morris, P., Weber, D.L., Sonkkilla, C., Shaw, M., Marcina, J., Tochon-Danguy, H., Egan, G., 2003. Cerebral function in posttraumatic stress disorder during verbal working memory updating: a positron emission tomography study. Biological Psychiatry 53, 474-481]. Frontal and parietal cortex are known to be involved in distributed networks for working memory processes, interacting with medial temporal areas during episodic memory processes. Abnormal function in these brain networks helps to explain everyday concentration and memory difficulties in PTSD. © 2005 Elsevier Ireland Ltd. All rights reserved.
169. Urrestarazu, E. and J. Iriarte, Mathematical analyses in the study of electroencephalographic signals. Análisis matemáticos en el estudio de señales electroencefalográficas, 2005. 41(7): p. 423-434.
Summary: Aim. The principal mathematical techniques applied to the EEG are reviewed. Development. After the introduction of digital EEG, new mathematical tools have been developed for the EEG analysis. Nowadays there are several techniques that analyse the EEG signal in different ways, getting a better understanding of the EEG: development of new montages; artifact removal; analysis in time domain, phase coherence and synchrony; source analysis; epileptic seizures detection and prediction; superposition of electrical activity and other neuroimaging techniques. Although they have demonstrated their efficacy, the comparison between them is not always easy. Conclusions. The development of mathematical tools for EEG analysis has improved the knowledge of the electric cerebral activity in normal and pathological conditions. They study many different aspects of the EEG signal. Their continuous development will produce an increase the knowledge of the normal and pathological cerebral functions. © 2005, Revista de Neurología.
170. Soufflet, L. and P.H. Boeijinga, Linear inverse solutions: Simulations from a realistic head model in MEG. Brain Topography, 2005. 18(2): p. 87-99.
Summary: Distributed linear solutions are widely used in source localization to solve the ill-posed EEG/MEG inverse problem. In the classical approach based on dipole sources, these methods estimate the current densities at a great number of brain sites, typically at the nodes of a 3-D grid which discretizes the chosen solution space. The estimated current density distributions are displayed as brain electromagnetic tomography (BET) images. We have tested well known minimum norm solutions (MN, WMN, LORETA) and other linear inverse solutions [WROP, sLORETA, interference uniform, gain uniform, weight vector normalized (WVN), and a new solution named SLF (Standardized Lead Field)], using a MEG configuration (BTi Magnes 2500 WH with 148 axial magnetometers) and a realistic head model using BEM (Boundary Element Method). The solutions were compared in a noise-free condition and in the presence of noise using the classical dipole localization errors (DLE) together with a new figure of merit that we called max gain uniformity, which measures the capability of an inverse linear solution to show spots of activity with similar amplitudes on the brain electromagnetic tomographies when multiple dipole sources with similar moments are simultaneously active. Whereas some solutions (sLORETA, interference uniform and SLF) were capable of zero dipole localization errors in the noise-free case, none of them reached 100% of correct dipole localizations in the presence of a high level of Gaussian noise. The SLF solution, which has the advantage to be independent from any regularisation parameter, presented the best results with the lowest max gain uniformities, with almost 100% of correct dipole localizations with 10% of noise and more than 90% of correct localizations with 30% of noise added to the data. Nevertheless, no solution was able to combine at the same time a correct localization of single sources and the capability to visualize multiple sources with comparable amplitudes on the brain electromagnetic tomographies. Copyright © 2005 Springer Science + Business Media, Inc.
171. Sekihara, K., M. Sahani, and S.S. Nagarajan, Localization bias and spatial resolution of adaptive and non-adaptive spatial filters for MEG source reconstruction. NeuroImage, 2005. 25(4): p. 1056-1067.
Summary: This paper discusses the location bias and the spatial resolution in the reconstruction of a single dipole source by various spatial filtering techniques used for neuromagnetic imaging. We first analyze the location bias for several representative adaptive and non-adaptive spatial filters using their resolution kernels. This analysis theoretically validates previously reported empirical findings that standardized low-resolution electromagnetic tomography (sLORETA) has no location bias. We also find that the minimum-variance spatial filter does exhibit bias in the reconstructed location of a single source, but that this bias is eliminated by using the normalized lead field. We then focus on the comparison of sLORETA and the lead-field normalized minimum-variance spatial filter, and analyze the effect of noise on source location bias. We find that the signal-to-noise ratio (SNR) in the measurements determines whether the sLORETA reconstruction has source location bias, while the lead-field normalized minimum-variance spatial filter has no location bias even in the presence of noise. Finally, we compare the spatial resolution for sLORETA and the minimum-variance filter, and show that the minimum-variance filter attains much higher resolution than sLORETA does. The results of these analyses are validated by numerical experiments as well as by reconstructions based on two sets of evoked magnetic responses. © 2004 Elsevier Inc. All rights reserved.
172. Sekihara, K., M. Sahani, and S.S. Nagarajan, A simple nonparametric statistical thresholding for MEG spatial-filter source reconstruction images. NeuroImage, 2005. 27(2): p. 368-376.
Summary: This paper proposes a simple statistical method for extracting target source activities from spatio-temporal source activities reconstructed from MEG measurements. The method requires measurements in a control condition, which contains only non-target source activities. The method derives, at each pixel location, an empirical probability distribution of the non-target source activity using the time course reconstruction obtained from the control period. The statistical threshold that can extract the target source activities is derived from the empirical distributions obtained from all pixel locations. Here, the multiple comparison problem is addressed with a two-step procedure involving standardizing these empirical distributions and deriving an empirical distribution of the maximum pseudo T value at each pixel location. The results of applying the proposed method to auditory-evoked measurements are presented to demonstrate the method's effectiveness. © 2005 Elsevier Inc. All rights reserved.
173. Schimpf, P.H., H. Liu, C. Ramon, and J. Haueisen, Efficient electromagnetic source imaging with adaptive standardized LORETA/FOCUSS. IEEE Transactions on Biomedical Engineering, 2005. 52(5): p. 901-908.
Summary: Functional brain imaging and source localization based on the scalp's potential field require a solution to an ill-posed inverse problem with many solutions. This makes it necessary to incorporate a priori knowledge in order to select a particular solution. A computational challenge for some subject-specific head models is that many inverse algorithms require a comprehensive sampling of the candidate source space at the desired resolution. Ia this study, we present an algorithm that can accurately reconstruct details of localized source activity from a sparse sampling of the candidate source space. Forward computations are minimized through an adaptive procedure that increases source resolution as the spatial estent is reduced. With this algorithm, we were able to compute inverses using only 6% to 11% of the full resolution lead-field, with a localization accuracy that was not significantly different than an exhaustive search through a fully-sampled source space. The technique is, therefore, applicable for use with anatomically-realistic, subject-specific forward models for applications with spatially concentrated source activity. © 2005 IEEE.
174. Saletu, B., P. Anderer, G.M. Saletu-Zyhlarz, D. Gruber, M. Metka, and J. Huber, Identifying target regions for vigilance improvement under hormone replacement therapy in postmenopausal syndrome patients by means of electroencephalographic tomography (LORETA). Psychopharmacology, 2005. 178(4): p. 389-399.
Summary: Rationale: Daytime fatigue, which at the neurophysiological level is due to vigilance decrements, is a frequent complaint in postmenopausal women. Objectives: In a three-arm, 2-month, parallel group-design study, vigilance-promoting effects of a novel continuous combination (=Climodien 2/3) of estradiol valerate (EV; 2 mg) and dienogest (DNG; 3 mg) were compared with the effects of both EV alone and placebo in 55 insomniac, postmenopausal syndrome patients. Methods: Low-resolution brain electromagnetic tomography (LORETA) was undertaken to identify the cerebral target regions of hormone replacement therapy. Results: An omnibus significance test revealed Climodien to increase activity in 882 of 2,394 voxels in the alpha-2 band, followed by 733, 706, and 664 voxels in the beta-2, beta-1, and beta-3 bands, and 509 voxels in the delta band, whereas 2 mg EV alone did not produce a significant suprathreshold activity. Current density increased predominantly in the right hemisphere, which had already been described in the literature as the center of the vigilance system. In the fast alpha range, which plays a major role in the context of vigilance, increased activity was found in the right prefrontal, temporal, and superior parietal cortices, i.e., those brain areas of the right-sided fronto-parietal neuronal network that are responsible for sustained attention. A further activity increase was seen in the anterior cingulate gyrus associated with attentional control and conflict monitoring. The right temporal lobe showed increased current density in all frequency bands. Conclusions: Electroencephalographic tomography (LORETA) identified the right-hemispheric vigilance system as the target region of Climodien. © Springer-Verlag 2004.
175. Pavlovsky, L., E. Seiffert, U. Heinemann, A. Korn, H. Golan, and A. Friedman, Persistent BBB disruption may underlie alpha interferon-induced seizures. Journal of Neurology, 2005. 252(1): p. 42-46.
Summary: Generalized seizures during Interferon-alpha (IFN-α) therapy have been repeatedly described in about 1 %-4 % of patients. However, the mechanisms underlying IFN-α induced seizures are not known. We describe a patient who developed partial and secondary generalized seizures during IFN-α therapy while displaying a focal disruption of her blood-brain barrier (BBB) corresponding with pathological electroencephalography (EEG). To test our hypothesis that IFN-α induces seizure activity, we exposed rat somatosensory cortices to clinically relevant concentrations of IFN-α in the acute in-vitro slice preparation or in-vivo. While acute exposure did not induce epileptic activity, recordings from slices exposed to IFN-α in-vivo one week prior to recordings revealed pronounced epileptiform activity in > 80 % of the slices. We propose that cortical exposure to IFN-α leads to the generation of an epileptic cortex, which explains the weeks of latency in patients from initial treatment to seizures, and stressing the importance of identifying possible BBB disruption among high-risk patients administered peripherally acting drugs.
176. Liu, H., P.H. Schimpf, G. Dong, X. Gao, F. Yang, and S. Gao, Standardized shrinking LORETA-FOCUSS (SSLOFO): A new algorithm for spatio-temporal EEG source reconstruction. IEEE Transactions on Biomedical Engineering, 2005. 52(10): p. 1681-1691.
Summary: This paper presents a new algorithm called Standardized Shrinking LORETA-FOCUSS (SSLOFO) for solving the electroencephalogram (EEG) inverse problem. Multiple techniques are combined in a single procedure to robustly reconstruct the underlying source distribution with high spatial resolution. This algorithm uses a recursive process which takes the smooth estimate of sLORETA as initialization and then employs the re-weighted minimum norm introduced by FOCUSS. An important technique called standardization is involved in the recursive process to enhance the localization ability. The algorithm is further improved by automatically adjusting the source space according to the estimate of the previous step, and by the inclusion of temporal information. Simulation studies are carried out on both spherical and realistic head models. The algorithm achieves very good localization ability on noise-free data. It is capable of recovering complex source configurations with arbitrary shapes and can produce high quality images of extended source distributions. We also characterized the performance with noisy data in a realistic head model. An important feature of this algorithm is that the temporal waveforms are clearly reconstructed, even for closely spaced sources. This provides a convenient way to estimate neural dynamics directly from the cortical sources. © 2005 IEEE.
177. Hong, B., H. Liu, P.H. Schimpf, S. Gao, and N.V. Thakor, Spatio-temporal analysis of P300 using ICA and SSLOFO. 2nd International IEEE EMBS Conference on Neural Engineering, 2005. 2005: p. 640-643.
Summary: Spatial information of EEG source activity revealed by inverse methods may contribute to an improvement of the BCI systems. This paper proposes an approach that integrates the Independent Component Analysis (ICA) and a newly developed inverse algorithm termed SSLOFO to robustly reconstruct cortical sources of P300. The target independent components are first extracted using a spatio-temporal optimization process and then SSLOFO is employed to localize the sources of the target components. Preliminary studies demonstrate our method is able to localize sources of P300 based on 5-trial-averaged EEG and the results are consistent with the findings of other functional imaging studies such as fMRI. The robustness of our approach is also proved by a study which indicates the P300 sources are stably reconstructed around the left and right TPJ areas. © 2005 IEEE.
178. He, B., High-resolution functional source and impedance imaging. Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings, 2005. 7 VOLS: p. 4178-4182.
Summary: Functional imaging has played a significant role in bettering our understanding of mechanisms of brain function and dysfunctions. We review recent research on electrophysiological neuroimaging, multimodal neuroimaging integrating functional MRI with EEG, and our development of magnetoacoustic tomography with magnetic induction for high resolution impedance imaging. Examples from research of our group will be shown to illustrate the concepts. The extensive work being pursued by a number of investigators suggests the promise of functional neuroimaging in imaging neural activity from noninvasive measurements. ©2005 IEEE.
179. Greenblatt, R.E., A. Ossadtchi, and M.E. Pflieger, Local linear estimators for the bioelectromagnetic inverse problem. IEEE Transactions on Signal Processing, 2005. 53(9): p. 3403-3412.
Summary: Linear estimators have been used widely in the bioelectromagnetic inverse problem, but their properties and relationships have not been fully characterized. Here, we show that the most widely used linear estimators may be characterized by a choice of norms on signal space and on source space. These norms depend, in part, on assumptions about the signal space and source space covariances. We demonstrate that two estimator classes (standardized and weight vector normalized) yield unbiased estimators of source location for simple source models (including only the noise-free case) but biased estimators of source magnitude. In the presence of instrumental (white) noise, we show that the nonadaptive standardized estimator is a biased estimator of source location, while the adaptive weight vector normalized estimator remains unbiased. A third class (distortionless) is an unbiased estimator of source magnitude but a biased estimatof of source location. © 2005 IEEE.
180. Durka, P.J., A. Matysiak, E.M. Montes, P.V. Sosa, and K.J. Blinowska, Multichannel matching pursuit and EEG inverse solutions. Journal of Neuroscience Methods, 2005. 148(1): p. 49-59.
Summary: We present a new approach to the preprocessing of the electroencephalographic time series for EEG inverse solutions. As the first step, EEG recordings are decomposed by multichannel matching pursuit algorithm - in this study we introduce a computationally efficient, suboptimal solution. Then, based upon the parameters of the waveforms fitted to the EEG (frequency, amplitude and duration), we choose those corresponding to the the phenomena of interest, like e.g. sleep spindles. For each structure, the corresponding weights of each channel define a topographic signature, which can be subject to an inverse solution procedure, like e.g. Loreta, used in this work. As an example, we present an automatic detection and parameterization of sleep spindles, appearing in overnight polysomnographic recordings. Inverse solutions obtained for single sleep spindles are coherent with the averages obtained for 20 overnight EEG recordings analyzed in this study, as well as with the results reported previously in literature as inter-subject averages of solutions for spectral integrals, computed on visually selected spindles. © 2005 Elsevier B.V. All rights reserved.
181. Dong, G., H. Liu, R.H. Bayford, R. Yerworth, P.H. Schimpf, and W. Yan, Spatial resolution improvement of 3D EIT images by the shrinking sLORETA-FOCUSS algorithm. Physiological Measurement, 2005. 26(2).
Summary: This paper describes the use of the shrinking sLORETA-FOCUSS algorithm to improve the spatial resolution of three-dimensional (3D) EIT images. Conventional EIT yields inaccurate, low spatial resolution images, due to noise, the low sensitivity of boundary voltages to inner conductivity perturbations and a limited number of boundary voltage measurements. The focal underdetermined system solver (FOCUSS) algorithm produces a localized energy solution based on the weighted minimum-norm least-squares (MNLS) solution. It was successfully applied for the spatial resolution improvement of EIT images of simulated and tank data for a 2D homogeneous circular disc. However, due to the fact that a 3D mesh system contains many more elements, much more memory is required to store the weighting matrix. In order to extend the work to 3D, the shrinking-FOCUSS method is utilized to shrink the solution space as well as the weighting matrix in each iteration step. The solution of the standardized low resolution electromagnetic tomography algorithm (sLORETA) is adopted as the initial estimate of the shrinking-FOCUSS. The effectiveness is verified by implementing the new algorithm on tank data for a three-dimensional homogeneous sphere. © 2005 IOP Publishing Ltd.
182. Bénar, C.G., R.N. Gunn, C. Grova, B. Champagne, and J. Gotman, Statistical maps for EEG dipolar source localization. IEEE Transactions on Biomedical Engineering, 2005. 52(3): p. 401-413.
Summary: We present a method that estimates three-dimensional statistical maps for electroencephalogram (EEG) source localization. The maps assess the likelihood that a point in the brain contains a dipolar source, under the hypothesis of one, two or three activated sources. This is achieved by examining all combinations of one to three dipoles on a coarse grid and attributing to each combination a score based on an F statistic. The probability density function of the statistic under the null hypothesis is estimated nonparametrically, using bootstrap resampling. A theoretical F distribution is then fitted to the empirical distribution in order to allow correction for multiple comparisons. The maps allow for the systematic exploration of the solution space for dipolar sources. They permit to test whether the data support a given solution. They do not rely on the assumption of uncorrelated source time courses. They can be compared to other statistical parametric maps such as those used in functional magnetic resonance imaging (fMRI). Results are presented for both simulated and real data. The maps were compared with LORETA and MUSIC results. For the real data consisting of an average of epileptic spikes, we observed good agreement between the EEG statistical maps, intracranial EEG recordings, and fMRI activations. © 2005 IEEE.
183. Auranen, T., A. Nummenmaa, M.S. Hämäläinen, I.P. Jääskeläinen, J. Lampinen, A. Vehtari, and M. Sams, Bayesian analysis of the neuromagnetic inverse problem with ℓp-norm priors. NeuroImage, 2005. 26(3): p. 870-884.
Summary: Magnetoencephalography (MEG) allows millisecond-scale non-invasive measurement of magnetic fields generated by neural currents in the brain. However, localization of the underlying current sources is ambiguous due to the so-called inverse problem. The most widely used source localization methods (i.e., minimum-norm and minimum-current estimates (MNE and MCE) and equivalent current dipole (ECD) fitting) require ad hoc determination of the cortical current distribution (ℓ2-, ℓ1-norm priors and point-sized dipolar, respectively). In this article, we perform a Bayesian analysis of the MEG inverse problem with ℓp-norm priors for the current sources. This way, we circumvent the arbitrary choice between ℓ1- and ℓ2-norm prior, which is instead rendered automatically based on the data. By obtaining numerical samples from the joint posterior probability distribution of the source current parameters and model hyperparameters (such as the ℓp-norm order p) using Markov chain Monte Carlo (MCMC) methods, we calculated the spatial inverse estimates as expectation values of the source current parameters integrated over the hyperparameters. Real MEG data and simulated (known) source currents with realistic MRI-based cortical geometry and 306-channel MEG sensor array were used. While the proposed model is sensitive to source space discretization size and computationally rather heavy, it is mathematically straightforward, thus allowing incorporation of, for instance, a priori functional magnetic resonance imaging (fMRI) information. © 2005 Elsevier Inc. All rights reserved.
184. Arrouët, C., M. Congedo, J.E. Marvie, F. Lamarche, A. Lécuyer, and B. Arnaldi, Open-ViBE: A three dimensional platform for real-time neuroscience. Journal of Neurotherapy, 2005. 9(1): p. 3-25.
Summary: Background. When the physiological activity of the brain (e.g., electroencephalogram, functional magnetic resonance imaging, etc.) is monitored in real-time, feedback can be returned to the subject and he/she can try to exercise some control over it. This idea is at the base of research on neurofeedback and brain-computer interfaces. Current advances in the speed of microprocessors, graphics cards and digital signal processing algorithms allow significant improvements in these methods. More meaningful features from the continuous flow of brain activation can be extracted and feedback can be more informative. Methods. Borrowing technology so far employed only in virtual reality, we have created Open-ViBE (Open Platform for Virtual Brain Environments). Open-ViBE is a general purpose platform for the development of three dimensional real-time virtual representations of brain physiological and anatomical data. Open-ViBE is a flexible and modular platform that integrates modules for brain physiological data acquisition, processing, and volumetric rendering. Results. When input data is the electroencephalogram, Open-ViBE uses the estimation of intra-cranial current density to represent brain activation as a regular grid of three dimensional graphical objects. The color and size of these objects co-vary with the amplitude and/or direction of the electrical current. This representation can be superimposed onto a volumetric rendering of the subject's MRI data to form the anatomical background of the scene. The user can navigate in this virtual brain and visualize it as a whole or only some of its parts. This allows the user to experience the sense of presence (being there) in the scene and to observe the dynamics of brain current activity in its original spatio-temporal relations. Conclusions. The platform is based on publicly available frameworks such as OpenMASK and OpenSG and is open source itself. In this way we aim to enhance the cooperation of researchers and to promote the use of the platform on a large scale. © 2005 by The Haworth Press, Inc. All rights reserved.
185. Wagner, M., M. Fuchs, and J. Kastner, Evaluation of sLORETA in the presence of noise and multiple sources. Brain Topography, 2004. 16(4): p. 277-280.
Summary: The standardized Low Resolution Brain Electromagnetic Tomography method (sLORETA) can be used to compute statistical maps from EEG and MEG data that indicate the locations of the underlying source processes with low error. These maps are derived by performing a location-wise inverse weighting of the results of a Minimum Norm Least Squares (MNLS) analysis with their estimated variances. In this contribution, we evaluate the performance of the method under the presence of noise and with multiple, simultaneously active sources. It is shown that the sLORETA method localizes well, as compared to other linear approaches such as MNLS and LORETA. However, simultaneously active sources can only be separated if their fields are distinct enough and of similar strength. In the context of a strong or superficial source, weak or deep sources remain invisible, and nearby sources of similar orientation tend not to be separated but interpreted as one source located roughly in between.
186. Moffitt, M.A. and W.M. Grill, Electrical localization of neural activity in the dorsal horn of the spinal cord: A modeling study. Annals of Biomedical Engineering, 2004. 32(12): p. 1694-1709.
Summary: Intraspinal microstimulation is a means of eliciting co-ordinated motor responses for restoration of function. However, detailed maps of the neuroanatomy of the human spinal cord are lacking, and it is not clear where electrodes should be implanted. We developed an electrical approach to localize active neurons in the spinal cord using potentials recorded from the surface of the spinal cord. We evaluated this localization method using an analytical model of the spinal cord and two previously developed inverse algorithms (standardized low resolution brain electromagnetic tomography (sLORETA) and a locally optimal source (LOS) method). The results support electrical source localization as a feasible imaging approach for localizing (within 300 μm) active neurons in the spinal cord. The LOS method could localize the source when 16 recording electrodes were placed on the dorsolateral aspect of the cord and the noise level was 2%. When recording electrodes were positioned around the entire circumference of the spinal cord, either localization method could localize the source, even at 15% noise. Finally, localization error was not sensitive to inaccuracies in the expected electrode positions or the electrical parameters of the forward model, but was sensitive to a geometrical modification of the forward model in one case.
187. Michel, C.M., M.M. Murray, G. Lantz, S. Gonzalez, L. Spinelli, and R. Grave De Peralta, EEG source imaging. Clinical Neurophysiology, 2004. 115(10): p. 2195-2222.
Summary: Objective: Electroencephalography (EEG) is an important tool for studying the temporal dynamics of the human brain's large-scale neuronal circuits. However, most EEG applications fail to capitalize on all of the data's available information, particularly that concerning the location of active sources in the brain. Localizing the sources of a given scalp measurement is only achieved by solving the so-called inverse problem. By introducing reasonable a priori constraints, the inverse problem can be solved and the most probable sources in the brain at every moment in time can be accurately localized. Methods and Results: Here, we review the different EEG source localization procedures applied during the last two decades. Additionally, we detail the importance of those procedures preceding and following source estimation that are intimately linked to a successful, reliable result. We discuss (1) the number and positioning of electrodes, (2) the varieties of inverse solution models and algorithms, (3) the integration of EEG source estimations with MRI data, (4) the integration of time and frequency in source imaging, and (5) the statistical analysis of inverse solution results. Conclusions and Significance: We show that modern EEG source imaging simultaneously details the temporal and spatial dimensions of brain activity, making it an important and affordable tool to study the properties of cerebral, neural networks in cognitive and clinical neurosciences. © 2004 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.
188. Galka, A., O. Yamashita, T. Ozaki, R. Biscay, and P. Valdés-Sosa, A solution to the dynamical inverse problem of EEG generation using spatiotemporal Kalman filtering. NeuroImage, 2004. 23(2): p. 435-453.
Summary: We present a new approach for estimating solutions of the dynamical inverse problem of EEG generation. In contrast to previous approaches, we reinterpret this problem as a filtering problem in a state space framework; for the purpose of its solution, we propose a new extension of Kalman filtering to the case of spatiotemporal dynamics. The temporal evolution of the distributed generators of the EEG can be reconstructed at each voxel of a discretisation of the gray matter of brain. By fitting linear autoregressive models with neighbourhood interactions to EEG time series, new classes of inverse solutions with improved resolution and localisation ability can be explored. For the purposes of model comparison and parameter estimation from given data, we employ a likelihood maximisation approach. Both for instantaneous and dynamical inverse solutions, we derive estimators of the time-dependent estimation error at each voxel. The performance of the algorithm is demonstrated by application to simulated and clinical EEG recordings. It is shown that by choosing appropriate dynamical models, it becomes possible to obtain inverse solutions of considerably improved quality, as compared to the usual instantaneous inverse solutions. © 2004 Elsevier Inc. All rights reserved.
189. Congedo, M., J.F. Lubar, and D. Joffe, Low-resolution electromagnetic tomography neurofeedback. IEEE Transactions on Neural Systems and Rehabilitation Engineering, 2004. 12(4): p. 387-397.
Summary: Through continuous feedback of the electroencephalogram (EEG) humans can learn how to shape their brain electrical activity in a desired direction. The technique is known as EEG biofeedback, or neurofeedback, and has been used since the late 1960s in research and clinical applications. A major limitation of neurofeedback relates to the limited information provided by a single or small number of electrodes placed on the scalp. We establish a method for extracting and feeding back intracranial current density and we carry out an experimental study to ascertain the ability of the participants to drive their own EEG power in a desired direction. To derive current density within the brain volume, we used the low-resolution electromagnetic tomography (LORETA). Six undergraduate students (three males, three females) underwent tomographic neurofeedback (based on 19 electrodes placed according to the 10-20 system) to enhance the current density power ratio between the frequency bands β (16-20 Hz) and a (8-10 Hz). According to LORETA modeling, the region of interest corresponded to the Anterior Cingulate (cognitive division). The protocol was designed to improve the performance of the subjects on the dimension of sustained attention. Two hypotheses were tested: 1) that the β/α current density power ratio increased over sessions and 2) that by the end of the training subjects acquired the ability of increasing that ratio at will. Both hypotheses received substantial experimental support in this study. This is the first application of an EEG inverse solution to neurofeedback. Possible applications of the technique include the treatment of epileptic foci, the rehabilitation of specific brain regions damaged as a consequence of traumatic brain injury and, in general, the training of any spatial specific cortical electrical activity. These findings may also have relevant consequences for the development of brain-computer interfaces.
190. Cannon, R., J. Lubar, K. Thornton, S. Wilson, and M. Congedo, Limbic beta activation and LORETA: Can hippocampal and related limbic activity be recorded and changes visualized using LORETA in an affective memory condition? Journal of Neurotherapy, 2004. 8(4): p. 5-24.
Summary: Background. The purpose of this study was to determine the validity of Low Resolution Electromagnetic Tomography (LORETA) in visualizing limbic structures and possibly identifying electroencephalographic (EEG) frequencies in the limbic region during an anger memory recall process. Method. This study was conducted with twelve subjects, non-clinical students at the University of Tennessee, Knoxville. A pre-study screening was conducted. Eyes-open baselines were obtained employing 300 epochs, or five minutes, using a 19-channel quantitative electroencephalographic (qEEG) acquisition system with linked ear reference. The experimental condition recording directly followed an eyes-open baseline. The experimental condition was to allocate a memory that created intense anger and retain the state as long as possible. All files were no less than 100 total epochs upon editing. The data were analyzed in both individual and group conditions with LORETA imaging software. Statistical differences between conditions were evaluated for significance, then computed and transformed into LORETA images. Results. The data revealed significant differences between the anger condition and baseline recordings in limbic structures and frontal regions. The data suggests that limbic lobe and hippocampal activity can be recorded and visualized using LORETA during affective memory recall. There are several notable differences between the baseline and condition images. One of the more interesting of these differences is possible activation of the amygdala, uncinate gyrus and surrounding structures in the beta (12-32 Hz) frequencies. The hemispheric asymmetries during anger memory recall offer further support for the lateralization of hemispheric activity relating to affective states. Conclusion. LORETA may be an effective method used to differentiate and visualize limbic lobe, hippocampal formation and other related structures during affective anger memory recall. © 2004 by The Haworth Press, Inc. All rights reserved.
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