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 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 (Hill et al., Neurology 45:1942–1943 1995; Ives et al., Electroencephalogr Clin Neurophysiol 87:417–420, 1993; Krakow et al., Brain 122(9):1679–1688, 1999b). 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. fMRI had been employed to study the haemodynamic correlates of seizures, relying on visual observation of the patient during seizure for interpretation of the BOLD signal changes. Ictal BOLD changes are, however, generally widespread, long lasting and difficult to interpret, particularly without concurrent EEG (Detre et al., Ann Neurol 38:618–624, 1995; Jackson et al., Neurology 54:524–527, 1994). Simultaneous EEG-fMRI can address this issue to better explain the haemodymaic changes at whole brain level for particular electrophysiological activity on EEG during seizures.