Focal magnetoencephalographic spikes in the superior temporal plane undetected by scalp EEG.

Temporal lobe spikes were detected by magnetoencephalography (MEG), but not by standard scalp electroencephalography (EEG), in a patient with intractable complex partial seizures. Simultaneous recording of scalp EEG and MEG revealed 2 different types of spike discharges: sporadic single spikes detected by both EEG and MEG which were localised diffusely in the right temporal lobe; and rhythmic MEG spike discharges that were not detected by scalp EEG, focally localised in the posterior part of the superior temporal plane. The tangential current orientation to the scalp may explain the different sensitivity of scalp EEG and MEG to rhythmic discharges. This study shows the unique sensitivity of MEG to epileptic activity in the superior temporal plane.