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EEG source reconstruction with spatio-temporal priors
e110
Society Proceedings / Clinical Neurophysiology 119 (2008) e99–e164
could be interpreted as TA influencing CBF or the existence of another physiologic variable influencing the CBF and the neuronal activity.
allow to disambiguate different ERP’s originating mechanisms. In visual-attention experimental data we found no evidences on phase resetting in the alpha band as reported previously by using ITC.
doi:10.1016/j.clinph.2008.04.058 doi:10.1016/j.clinph.2008.04.060
43. The resting state: Relations between EEG rhythms and fMRI networks—P. Ritter (Germany) Even in the absence of explicit external or internal stimuli, the brain sustains its activity in a characteristic way, which reveals a distinct resting state network (RSN) of confined anatomical structures as measured by fMRI. Simultaneous recording of EEG and fMRI allows assessing fMRI correlates of these background rhythms. Particularly the alpha (8–12 Hz) and beta (13–29 Hz) rhythms have been extensively evaluated by simultaneous EEG–fMRI. fMRI correlates of both rhythms have been found in anatomical structures that correspond to those of the RSNs. It has further been shown that certain spectral bands, such as alpha, contain multiple functionally distinct EEG rhythms with specific scalp distributions. Based on this knowledge we hypothesized that RSN temporal properties are related to those of the distinct background rhythms. We test this hypothesis on resting state data acquired under eyes closed and eyes open conditions with simultaneous EEG–fMRI. Beyond presentation of interim results we aim at discussing different analysis approaches of integrating data from both modalities. A methodological challenge of simultaneous EEG– fMRI acquisition, in particular residual gradient artifacts and ballistocardiogram can affect results and easily lead to illegitimate inference. doi:10.1016/j.clinph.2008.04.059
44. Exploring event related brain dynamics with test on complex valued time-frequency representations—E. Martı´nez Montes, E. Cuspineda, W. El deredy, J.M. Sa´nchez Bornot, A. Lage Castellanos, P.A. Valde´s Sosa (Cuba) Finding the originating mechanisms of the neurophysiological ERP is crucial for the understanding of cognitive and pathological brain functioning. Wavelet transformation of EEG trials provides complex coefficients for each frequency and latency, whose absolute values relates to the amplitudes and angles to the phases of oscillations. We propose t-like statistics for testing changes(w.r.t baseline) in the (i) mean value of the coefficients, (ii) variance of their absolute values around the mean, (iii) Intertrial Coherence (ITC) and (iv) concentration of phases. In the latter case two different tests are introduced: equality of eigenvalues of the covariance matrix (real vs. Imaginary part) and the second trigonometric moment of the bimodal distribution of phases that appears after removing the mean. Simulated data sets of an ERP originated by phase resetting and by an additive component, allowed to successfully validate the proposed tests for measuring corresponding effects. Also, we found that ITC is not appropriate for evaluating phase reorganization as origin of ERP since it depends on the mean activity. Proposed tests for concentration of phases
45. Bayesian M/EEG source reconstruction with spatiotemporal priors—N.J. Trujillo Barreto, E. Aubert Va´zquez, W.D. Penny (Cuba) 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. The experimental design can be coded in a design matrix, effects of interest characterised using contrasts and inferences made using posterior probability maps. 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 analyse an EEG data set from a face processing experiment. We demonstrate that by explicitly modelling neuronal activity dynamics one can obtain better source reconstructions. The computational simplicity of fitting glms, allied to the efficiency of variational inference, results in a relatively fast algorithm. Also, the GLM can accommodate damped sinusoidal and wavelet approaches that are ideal for modeling transient and nonstationary responses. doi:10.1016/j.clinph.2008.04.061
46. Neurophysiology and neuroscience in Cuban national programme on handicapped people and brain disorders—M. Valde´s Sosa (Cuba) Cuba has developed in recent years a program for the care of disabled people with complete coverage for the whole nation, of which the framework is explained in this talk. This program is concerned with not only with medical aspects, but also with social, labor, and educational facets. Cuban neurophysiology and clinical neuroscience (specifically the national network of neuroscience labs) has participated in this program developing cost-effective methods for the early screening, detection and diagnosis of disabilities due to brain dysfunction. This has represented a large investment in translational research. An attempt has been made to reconcile two apparently unconnected goals: (1) reaching in the short term clear health benefits for specific groups of disabled people; and (2) taking advantage of large population-based studies to further the understanding of the underlying mechanisms of brain dysfunction. Work targeted
Society Proceedings / Clinical Neurophysiology 119 (2008) e99–e164
could be interpreted as TA influencing CBF or the existence of another physiologic variable influencing the CBF and the neuronal activity.
allow to disambiguate different ERP’s originating mechanisms. In visual-attention experimental data we found no evidences on phase resetting in the alpha band as reported previously by using ITC.
doi:10.1016/j.clinph.2008.04.058 doi:10.1016/j.clinph.2008.04.060
43. The resting state: Relations between EEG rhythms and fMRI networks—P. Ritter (Germany) Even in the absence of explicit external or internal stimuli, the brain sustains its activity in a characteristic way, which reveals a distinct resting state network (RSN) of confined anatomical structures as measured by fMRI. Simultaneous recording of EEG and fMRI allows assessing fMRI correlates of these background rhythms. Particularly the alpha (8–12 Hz) and beta (13–29 Hz) rhythms have been extensively evaluated by simultaneous EEG–fMRI. fMRI correlates of both rhythms have been found in anatomical structures that correspond to those of the RSNs. It has further been shown that certain spectral bands, such as alpha, contain multiple functionally distinct EEG rhythms with specific scalp distributions. Based on this knowledge we hypothesized that RSN temporal properties are related to those of the distinct background rhythms. We test this hypothesis on resting state data acquired under eyes closed and eyes open conditions with simultaneous EEG–fMRI. Beyond presentation of interim results we aim at discussing different analysis approaches of integrating data from both modalities. A methodological challenge of simultaneous EEG– fMRI acquisition, in particular residual gradient artifacts and ballistocardiogram can affect results and easily lead to illegitimate inference. doi:10.1016/j.clinph.2008.04.059
44. Exploring event related brain dynamics with test on complex valued time-frequency representations—E. Martı´nez Montes, E. Cuspineda, W. El deredy, J.M. Sa´nchez Bornot, A. Lage Castellanos, P.A. Valde´s Sosa (Cuba) Finding the originating mechanisms of the neurophysiological ERP is crucial for the understanding of cognitive and pathological brain functioning. Wavelet transformation of EEG trials provides complex coefficients for each frequency and latency, whose absolute values relates to the amplitudes and angles to the phases of oscillations. We propose t-like statistics for testing changes(w.r.t baseline) in the (i) mean value of the coefficients, (ii) variance of their absolute values around the mean, (iii) Intertrial Coherence (ITC) and (iv) concentration of phases. In the latter case two different tests are introduced: equality of eigenvalues of the covariance matrix (real vs. Imaginary part) and the second trigonometric moment of the bimodal distribution of phases that appears after removing the mean. Simulated data sets of an ERP originated by phase resetting and by an additive component, allowed to successfully validate the proposed tests for measuring corresponding effects. Also, we found that ITC is not appropriate for evaluating phase reorganization as origin of ERP since it depends on the mean activity. Proposed tests for concentration of phases
45. Bayesian M/EEG source reconstruction with spatiotemporal priors—N.J. Trujillo Barreto, E. Aubert Va´zquez, W.D. Penny (Cuba) 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. The experimental design can be coded in a design matrix, effects of interest characterised using contrasts and inferences made using posterior probability maps. 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 analyse an EEG data set from a face processing experiment. We demonstrate that by explicitly modelling neuronal activity dynamics one can obtain better source reconstructions. The computational simplicity of fitting glms, allied to the efficiency of variational inference, results in a relatively fast algorithm. Also, the GLM can accommodate damped sinusoidal and wavelet approaches that are ideal for modeling transient and nonstationary responses. doi:10.1016/j.clinph.2008.04.061
46. Neurophysiology and neuroscience in Cuban national programme on handicapped people and brain disorders—M. Valde´s Sosa (Cuba) Cuba has developed in recent years a program for the care of disabled people with complete coverage for the whole nation, of which the framework is explained in this talk. This program is concerned with not only with medical aspects, but also with social, labor, and educational facets. Cuban neurophysiology and clinical neuroscience (specifically the national network of neuroscience labs) has participated in this program developing cost-effective methods for the early screening, detection and diagnosis of disabilities due to brain dysfunction. This has represented a large investment in translational research. An attempt has been made to reconcile two apparently unconnected goals: (1) reaching in the short term clear health benefits for specific groups of disabled people; and (2) taking advantage of large population-based studies to further the understanding of the underlying mechanisms of brain dysfunction. Work targeted