Cortical connectivity in fronto-temporal focal epilepsy from EEG analysis: A study via graph theory

Focal epilepsies are associated to the dysfunction of a pathological neuronal network (epileptic network) rather than to a single epileptogenic region. Simultaneous electroencephalogram (EEG)functional MRI (EEG-fMRI) allows identification of hemodynamic networks associated with interictal epileptiform discharges (IEDs). Better understanding of interactions between physiological and epileptic networks, as well as exploring how this interaction is influenced by IEDs, is fundamental, considering the increasing volume of resting state functional connectivity studies. In recent works we found that drug-resistant epilepsy involves a durable non-transient re-arrangement of brain functional connectivity patterns that are present in absence of visible scalp IEDs. These are specific for each patient and occur also in non-lesional cases. The epileptic network could be considered as a new or modified ‘‘physiological” resting state networks (RSNs), additionally activated by the occurrence of IEDs. This hypothesis of new pathological RSN is corroborated by the fact that epileptic functional connectivity maps do not share the topographic pattern of typically described RSN. We can hypothesize that these epileptic networks may evolve over time from transient to more permanent connectivity changes as a result of plasticity triggered by pathological activity. How this finding impact the (re)-organization of the known physiological RSNs remains to be elucidated.