title: A systems-level approach to human epileptic seizures.
abstract: Epileptic seizures are due to the pathological collective activity of large cellular assemblies. A better understanding of this collective activity is integral to the development of novel diagnostic and therapeutic procedures. In contrast to reductionist analyses, which focus solely on small-scale characteristics of ictogenesis, here we follow a systems-level approach, which combines both small-scale and larger-scale analyses. Peri-ictal dynamics of epileptic networks are assessed by studying correlation within and between different spatial scales of intracranial electroencephalographic recordings (iEEG) of a heterogeneous group of patients suffering from pharmaco-resistant epilepsy. Epileptiform activity as recorded by a single iEEG electrode is determined objectively by the signal derivative and then subjected to a multivariate analysis of correlation between all iEEG channels. We find that during seizure, synchrony increases on the smallest and largest spatial scales probed by iEEG. In addition, a dynamic reorganization of spatial correlation is observed on intermediate scales, which persists after seizure termination. It is proposed that this reorganization may indicate a balancing mechanism that decreases high local correlation. Our findings are consistent with the hypothesis that during epileptic seizures hypercorrelated and therefore functionally segregated brain areas are re-integrated into more collective brain dynamics. In addition, except for a special sub-group, a highly significant association is found between the location of ictal iEEG activity and the location of areas of relative decrease of localised EEG correlation. The latter could serve as a clinically important quantitative marker of the seizure onset zone (SOZ).
authors.affiliation: Support Center for Advanced Neuroimaging, University Institute of Diagnostic and Interventional Neuroradiology, Inselspital, Bern University Hospital, University of Bern, 3010, Bern, Switzerland. crummel@web.de
authors.forename: Christian
authors.initials: C
authors.lastname: Rummel
authors.forename: Marc
authors.initials: M
authors.lastname: Goodfellow
authors.forename: Heidemarie
authors.initials: H
authors.lastname: Gast
authors.forename: Martinus
authors.initials: M
authors.lastname: Hauf
authors.forename: Frédérique
authors.initials: F
authors.lastname: Amor
authors.forename: Alexander
authors.initials: A
authors.lastname: Stibal
authors.forename: Luigi
authors.initials: L
authors.lastname: Mariani
authors.forename: Roland
authors.initials: R
authors.lastname: Wiest
authors.forename: Kaspar
authors.initials: K
authors.lastname: Schindler
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D001921:Brain / Q000473:pathology / Q000503:physiopathology; D058256:Brain Waves / Q000502:physiology*; D004569:Electroencephalography; D004827:Epilepsy / Q000175:diagnosis* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008954:Models, Biological; D018709:Statistics, Nonparametric