Space–time network connectivity and cortical activations preceding spike wave discharges in human absence epilepsy: a MEG study
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To describe the spatial and temporal profiles of connectivity networks and sources preceding generalized spike-and-wave discharges (SWDs) in human absence epilepsy. Nonlinear associations of MEG signals and cluster indices obtained within the framework of graph theory were determined, while source localization in the frequency domain was performed in the low frequency bands with dynamic imaging of coherent sources. The results were projected on a three-dimensional surface rendering of the brain using a semi-realistic head model and MRI images obtained for each of the five patients studied. An increase in clustering and a decrease in path length preceding SWD onset and a rhythmic pattern of increasing and decreasing connectivity were seen during SWDs. Beamforming showed a consistent appearance of a low frequency frontal cortical source prior to the first generalized spikes. This source was preceded by a low frequency occipital source. The changes in the connectivity networks with the onset of SWDs suggest a pathologically predisposed state towards synchronous seizure networks with increasing connectivity from interictal to preictal and ictal state, while the occipital and frontal low frequency early preictal sources demonstrate that SWDs are not suddenly arising but gradually build up in a dynamic network.
KeywordsSpike wave discharge Absence epilepsy Nonlinear association analysis Beamforming Magnetoencephalography Connectivity Small world networks
This study was funded by the Netherlands Organization for Scientific Research (NWO), Grant number 400-04-483 to GvL and PO. We would like to thank Prof. Dr. P. Fries and co-workers for their hospitality at the Donders Center for Neuroimaging, Nijmegen, the Netherlands.
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