LAUSR

Commentary Both magnetoencephalography (MEG) and stereo-EEG (sEEG) have been in use for a number of years and are now considered the workhorses of presurgical evaluation of patients with treatment-resistant epilepsies. As a reminder, MEG noninvasively measures magnetic fields produced by electric charges moving from one point to another with the directionality of the current flow determined by the right-hand rule (1). Of importance are several features of the MEG recordings—the strength of the signal is inversely proportional to the distance from the detector (i.e., deeper sources are more difficult to detect), signal detection is best from sources tangential to the skull with sources that are purely orthogonal (basically not detectable); of importance is the fact there may be multiple electrical sources of epileptiform discharges in the brain that may be clinically important—these and other features, such as dipole clustering, are important for the correlation between MEG and sEEG and for surgical outcomes as examined in the manuscript by Murakami et al. The results of MEG, when epileptiform discharges are detected, have an overall fairly high chance of influencing the decision regarding placement Correlating Magnetoencephalography to Stereo-Electroencephalography in Patients Undergoing Epilepsy Surgery.