Combining EEG and FMRI in epilepsy: methodological challenges and clinical results

It is now possible to combine continuous recording of the EEG and continuous functional MRI scanning. This makes it possible to determine the regions of the brain showing changes in the fMRI signal in response to epileptic spikes occurring in the EEG. This article reviews the experience with this method in more than 100 studies performed over the last 4 years at the Montreal Neurological Institute. The technique is complex, and the authors review the various issues related to obtaining a good-quality EEG in the hostile environment of the magnetic resonance scanner, the statistical analysis of magnetic resonance images, in particular the issue of knowing what is the hemodynamic response function appropriate for the analysis of epileptic spikes, and the combination of EEG and fMRI results. The difficult theoretical issues raised by the interpretation of activation and deactivation, both frequently seen in response to spikes, are discussed. Finally, the authors give examples of fMRI responses seen with focal spikes and with generalized spike and wave discharges.