Pre-seizure architecture of the local connections of the epileptic focus examined via graph-theory

Abstract

Objective: Epilepsy is characterized by unpredictable and sudden paroxysmal neuronal firing occurrences and sometimes evolving in clinically evident seizure. To predict seizure event, small-world characteristic in nine minutes before seizure, divided in three 3-min periods (T0, T1, T2) were investigated.

Methods: Intracerebral recordings were obtained from 10 patients with drug resistant focal epilepsy examined by means of stereotactically implanted electrodes; analysis was focused in a period of low spiking (Baseline) and during two seizures. Networks' architecture is undirected and weighted. Electrodes' contacts close to epileptic focus are the vertices, edges are weighted by mscohere (=magnitude squared coherence).

Results: Differences were observed between Baseline and T1 and between Baseline and T2 in theta band; and between Baseline and T1, Baseline and T2, and near-significant difference between T0 and T2 in Alpha 2 band. Moreover, an intra-band index was computed for small worldness as difference between Theta and Alpha 2. It was found a growing index trend from Baseline to T2.

Conclusions: Cortical network features a specific pre-seizure architecture which could predict the incoming epileptic seizure.

Significance: Through this study future researches could investigate brain connectivity modifications approximating a clinical seizure also in order to address a preventive therapy.

Keywords: Epilepsy; Functional connectivity; Graph theory; Seizure; Small-world; eLORETA; sEEG.