Abstracts

Rationale: The growing body of evidence demonstrates that to gain insight into mechanisms of epilepsy requires understanding of the complex interactions between the individual components of the epileptic network. The main aim of this study was to elucidate the functional organization and temporal dynamics of neocortical irritative zone generating interictal epileptiform discharges (IEDs).Methods: A novel algorithm and protocol to characterize and quantify the network organization from the spatial distribution of low amplitude IEDs has been developed and involved following main steps: detection of single low amplitude IEDs; grouping of simultaneously occurring IEDs into multichannel IED event; identification and extraction of existing spatial profiles of IED events; sorting of the IED events according to identified spatial profiles using Principal Component Analysis; and quantitative post-processing.Results: Application of the algorithm to intracranial recordings of 14 patients with refractory neocortical epilepsy demonstrated that IEDs emerged from the heterogeneous network composed of multiple independent sub-regions (11±6 per patient) each with specific spatial profile, dynamics and amount of generated epileptic activity. The most active sub-region co-localized with seizure onset zone in 12/14 patients and had spatial overlap of 49±28%. Resection of all sub-regions with >12% contribution to generated IEDs was associated with seizure-free outcome (p=0.011). The activity of the irritative network was determined by the long-term fluctuations of sub-region properties governed mainly by circadian rhythms. Average occurrence of IEDs in wakefulness is 48±33% of sleep occurrence. On the contrary, 23% of sub-regions increased their activity during wakefulness.Conclusions: This study demonstrates that individual components of the irritative zone are not uniformly important for its organization, spatiotemporal dynamics and for delineating the extent of surgical resection. Ability to stratify the irritative zone increases the diagnostic yield of intracranial investigations and has potential to improve the results of surgical treatment in neocortical epilepsy patients. Acknowledgement: This work has been supported by grants from Ministry of Health of the Czech Republic, NT/14489-3 and 15-29835A.