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

OBJECTIVE To identify features of BOLD signal change associated with interictal epileptiform discharges (IEDs) in a heterogeneous group of focal epilepsy patients. METHODS EEG/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. RESULTS fMRI 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. CONCLUSION Despite 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. SIGNIFICANCE There 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.