EEG–fMRI in Adults with Focal Epilepsy

Abstract

The application of EEG-correlated fMRI (EEG–fMRI) in adults with focal epilepsy has two principal aims: to improve our understanding of the generators of epileptiform activity and to improve the surgical treatment of epilepsy. EEG–fMRI, except in unusual circumstances (Salek-Haddadi et al. 2003; Kobayashi et al. 2006d), has been used to study scalp interictal epileptiform discharges (IEDs). The relative abundance of IEDs (and the lack of associated clinical manifestations) drove the initial development of EEG–fMRI with a view to studying the fMRI signal changes associated with epileptic activity (Ives et al. 1993; Hill et al. 1995; Huang-Hellinger et al. 1996). Previously, fMRI had been employed to study the haemodynamic correlates of seizures, relying on visual observation of the patient for interpretation of the BOLD signal changes. Ictal BOLD changes are, however, generally widespread, long lasting and difficult to interpret, particularly without concurrent EEG (Jackson et al. 1994; Detre et al. 1995, 1996; Krings et al. 2000; see Salek-Haddadi et al. 2003 for review). Analysis of scalp IEDs is not without its problems. Scalp IEDs may reflect propagated activity rather than the source. Furthermore, even when the scalp IEDs are representative of the source or sources, there are no unique solutions to the generator location problem, and such solutions depend upon critical assumptions (such as the number of sources). EEG–fMRI is free from such assumptions and may therefore give a more accurate indication of the source or sources of IEDs.