Abstracts

Rationale: Focal epilepsies are associated to dysfunction of a pathological neuronal network (epileptic network) rather than to a single focus. Simultaneous EEG-fMRI allows the identification of networks associated with interictal epileptiform discharges (IEDs). However, the preservation of network structure between the occurrence of IEDs and its role in brain functional organization are still poorly understood. The aims of this study were to assess if the epileptic networks exhibit coherent fluctuations independent from the occurrence of scalp-detected IEDs and to investigate the patient-network specificity.Methods: We acquired EEG-fMRI resting state in 8 drug-resistant focal epilepsy patients, having multifocal IED-correlated BOLD response and maximal t-value in the IEDs field. For each patient, we performed Functional Connectivity (FC) seeded from the statistical maximum from IED-correlated analysis.We compared the FC-maps before and after regressing out the effect of IEDs in terms of statistical power (max and mean t-values) and of percentage of spatial overlap. In each patient we tested for epileptic network specificity, using resting state fMRI of 20 healthy subjects, matched for age. In these controls, we obtained the FC maps based on the patient-seed and we evaluated the difference between each patient and the group of healthy subjects (Wilcoxon rank-sum test). Finally, we built the commonality map of each group of controls and we looked for the patterns specificity between the subjects and the patients.Results: At group level, the FC map mean and max t-values were significantly reduced (p<0.01) after regressing out the IEDs, but the spatial extent of the maps were very similar with a spatial overlap of . Each patient showed a seed-based FC map statistically different (p<0.001) from healthy controls. In particular, we observed regions with increased ipsilateral, but decreased contralateral connectivity with respect to the IEDs focus.Conclusions: Epilepsy involves a durable non-transient rearrangement of brain functional connectivity patterns that is present in absence of visible scalp IEDs. These are specific for each patient and occur also in no lesional cases. How this finding impacts the (re)-organisation of the known physiological RSNs remains to be elucidated.