Simultaneous electroencephalography and functional magnetic resonance imaging applied to epilepsy.

Among the recent advances in neuroimaging and clinical neurophysiology, simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), that is SEM, stands apart as a challenging integration of techniques with great potential to provide unique information. The benefit of this integration is the utilization of each technique's strengths: the high temporal resolution and sensitivity to epileptic abnormalities of EEG and the high spatial resolution and noninvasive localization of cerebral metabolic change of fMRI. With SEM, electroencephalographic events that occur during fMRI may be identified and subsequently mapped with high resolution according to the hemodynamic changes that accompany them. Reaching the point of technically reliable SEM has required solutions to the many safety and electrical noise problems inherent to this technique. Recording an electroencephalogram during MRI requires special, MRI-compatible EEG equipment and a means to identify the low-amplitude electroencephalographic signal within an electrically noisy environment. With the results obtained at several institutions, SEM is now at a point in its development where the understanding of its validity as an indicator of the epileptic irritative and ictal-onset zones can be expanded. Because of its integration of both electrophysiologic and metabolic information, SEM also may be used to gain a greater understanding of cerebral physiology, in general, and fundamental aspects of epilepsy, in particular.