Display of consistent ictal networks in refractory mesial temporal lobe epilepsy

Exploration of emergent ictal networks was performed in homogeneous subjects with refractory medial temporal lobe epilepsy.

Maximal Synchrony Index (SI) values were calculated for all electrode pairs for each second during 25 seizures and displayed as connectivity animations. Consistent temporal patterns of SI value and spatial connectivity were observed across seizures and subjects, and used to define a sequence of network stages.

Highest SI values were found in electrodes within the area of surgical resection. Analysis of these electrodes by network stage demonstrated lateral temporal cortex dominance at seizure initiation, giving way to hippocampal synchrony during the major portion of the seizure, with lateral temporal regions re-emerging as the seizure terminated. SI values also corresponded to behavioral severity of seizures, and lower SI values were associated with post-surgical seizure freedom.

SI based methods of network characterization consistently display the intrinsic MTLE ictal network and may be sensitive to clinical features.

Consistency of EEG-derived network patterns is an important step as network features are applied towards improvement of clinical management. These data confirm consistency of network patterns within and across subjects and support the potential for these methods to distinguish relevant clinical variables.