Abstracts

Rationale: Intrinsic spontaneous brain activity is represented by the continuously fluctuating activity of physiological resting state networks (RSNs) related to various sensory and behavioral functions, as shown by coherent fluctuations of blood-oxygen-level dependent (BOLD) signal using functional MRI (fMRI). It has been demonstrated that epileptic activity arises from the dysfunction of a neuronal pathological network (epileptic network) rather than from a single focal source. Simultaneous electroencephalography (EEG)-fMRI can be used to map these networks. The aim of this study was to assess if epileptic networks, revealed by IED-correlated BOLD changes, exhibit coherent fluctuations independently of the occurrence of IEDs on scalp EEG. Methods: We included resting state EEG-fMRI dataset (3Tesla) acquired on seven patients with drug resistant focal epilepsy, having multifocal BOLD response to IEDs and maximal t-value corresponding to the IED field. We excluded patients with epileptic focus in the default mode network. Functional connectivity (FC) was computed from a 6 mm sphere drawn in the region of maximal t-value of the IEDs-related BOLD maps. In a second step, FC was re-computed with IEDs used as confounds. Single subject FC maps (p <0.001 uncorrected) with and without removing the effect of the IED were visually examined and compared. Results: FC analysis showed a similar epileptic network compared to spike-related BOLD maps. FC maps were largely preserved after regressing out the effect of the scalp IEDs. Conclusions: Regions involved in a specific epileptic network show functional coupling beyond the occurrence of interictal activity. Beyond supporting the presence of epileptic activity invisible to the scalp, these networks can be seen as pathological intrinsic fluctuations of BOLD signal, in the sense of new or modified RSN. The interactions between these epilepsy-specific RSNs, the physiological RSNs and behavioral performances remain to be elucidated. This work was supported by Swiss National Science Foundation grants 140332 (SPUM Epilepsy) and 141165.