EEG–fMRI in focal epilepsy: Local activation and regional networks

•EEG/fMRI is an important new tool for studying patients with focal epilepsy and the electrographic field of the interictal epileptiform discharges (IEDs) is reflected in the fMRI results with focal and diffuse IEDs providing novel and important localization information.•Amongst patients with a heterogeneous array of focal epilepsies, the piriform cortex is a common node in the underlying networks associated with focal IEDs.•In cases of diffuse IEDs we noted involvement of subcortical structures, in particular the thalamus and cerebellum.

ObjectiveTo identify features of BOLD signal change associated with interictal epileptiform discharges (IEDs) in a heterogeneous group of focal epilepsy patients.MethodsEEG/fMRI studies in 27 focal epilepsy patients were reviewed with attention given to the extent and location of the IED and the resulting pattern of BOLD signal change. Second order group analysis was used to identify common features.ResultsfMRI results provided novel clinical information for individual patients. We identified a significant common node within the ipsilateral piriform cortex as well as patterns involving distant cortical or subcortical areas.ConclusionDespite the heterogeneity of IEDs in focal epilepsy, there are important common features underpining IEDs with a highly significant fMRI node in the ipsilateral piriform cortex.SignificanceThere are important common features in the networks involved in IEDs in patients with a heterogeneous range of epileptogenic foci. We confirm that the piriform cortex is a common node underlying IEDs in patients with focal epilepsy and so provides a target for further study and potential therapy. We describe important features of BOLD signal change that accompany focal and diffuse IEDs that will help researchers and clinicians navigate the sometimes complex findings revealed by these studies.