Spatiotemporal dynamics of interictal spikes

The relationship of epileptic spikes to seizures has been a matter of debate with researchers reporting higher or lower spike rates before and after seizures. To elucidate a possible role of spikes in ictogenesis (seizure generation) we developed a mathematical framework to investigate the spatiotemporal dynamics of spikes in the epileptic brain. Long-term (5-10 days) intracranial electroencephalograms (iEEGs) from 2 patients with temporal lobe epilepsy who underwent presurgical evaluation for localization of candidate epileptic foci were used in the study. First, spikes were detected using an in-house spike detection algorithm. To characterize the spatiotemporal changes in spikes a novel spatial synchronization measure (SSM) of spikes was developed. Application of SSM to iEEG revealed monotonically increasing long-term preictal synchronization between spike trains at brain sites that included the epileptogenic zone. The presence of preictal synchronization of spikes hours to minutes prior to the onset of seizures indicates a possible predictive value of spike synchronization for seizure occurrence. Furthermore, across seizures and patients, we observed that desynchronization of spikes at critical brain sites mostly occurred in postictal epochs. We characterized these observed changes between preictal and postical spike synchronization by a measure of resetting based on the fraction of pairs that synchronize preictally and desynchronize postictally. On the basis of this resetting measure, we showed that resetting of spike synchronization occurs more commonly at seizures than interictally (p Keywords: Epilepsy, Spikes, Seizures, Spatiotemporal Analysis, Ictogenesis
INTRODUCTION Epilepsy is a widely prevalent neurological disorder affecting around 50 million people worldwide and has been classified as the third most common neurological disorder next to stroke and Alzheimer's. [...]