APPARENT ASYNCHRONY BETWEEN INTERICTAL ELECTRIC AND MAGNETIC SPIKES

WE recorded simultaneous multichannel electroencephalogram (EEG) and m agnetoencephalogram (MEG) in four children with partial epilepsy. Sour ces of averaged spikes were modelled with current dipoles. Of 10 spike averages obtained, three peaked simultaneously in MEG and EEG, and in seven averages, the MEG peak preceded the main EEG peak by 9-40 ms. A small positive early EEG signal coincided with the MEG peak in six as ynchronous spikes. The simultaneous MEG and EEG spikes originated with in 5-23 mm, while sources of asynchronous peaks were 12-67 mm apart. W e conclude that non-identical neurone currents underlie the MEG and EE G signals, and emphasize the importance of modelling early phases of E EG spikes when localizing interictal epileptic zones.