Strong “intrinsic” functional connectivity of epileptic networks independent of scalp interictal epileptiform EEG discharges

Abstract

Objective Epileptic activity arises from dysfunction of pathological neuronal network (epileptic network). Aim: to assess maintenance of epileptic network in between IEDs occurrence. Methods We acquired simultaneous EEG-fMRI resting state in 10 drug-resistant focal epilepsy patients, having multifocal BOLD response and maximal t -value in the IED field. We compared results of functional connectivity (FC) before and after removing IEDs effect for two seed types: a 10mm-diameter sphere drawn in the BOLD map maximum and the epileptic component obtained by Indipendent component analysis. We evaluated the results in terms of mean t -value and the percentage of overlap between the FC maps. Results Mean t -value was significant lower after regressing out the IEDs at group level ( p = 0.008 for sphere; p = 0.0004 for epileptic component). Overlap extent was 85% ± 12% and 87% ± 12% for the sphere and the epileptic component, respectively. Conclusions Regions involved in a specific epileptic network show coherent oscillation independent of the occurrence of interictal activity. This could indicate the presence of epileptic activity invisible to the scalp-EEG or the presence of new and pathological resting state networks. Key message Regions involved in a specific epileptic network show functional coupling independently of the occurrence of interictal activity as revealed on scalp EEG.