Combining MEG and EEG Source Modeling in Epilepsy Evaluations

This article reviews the relative strengths and weaknesses of MEG and EEG source modeling for localization of epileptogenic foci. Proper interpretation of these dipole models requires an appreciation for the limitations of each technique and an understanding of the character of the cortical sources that can generate epileptiform transients identifiable in recordings of spontaneous cerebral activity. MEG is sensitive to smaller sources, is not altered by the skull and scalp, requires a simpler head model, and provides more accurate localization, but it is insensitive to radial sources. EEG requires larger sources, is attenuated and smeared by the skull/scalp, requires a more complicated head model, and provides less accurate localization; however, and most importantly, it is sensitive to all source orientations. In conclusion, the case is made that maximal clinical information is obtained when simultaneous MEG and EEG are both subjected to source modeling, either individually or in a combined fashion.