POSSIBILITIES AND LIMITATIONS OF MAGNETIC SOURCE IMAGING OF METHOHEXITAL-INDUCED EPILEPTIFORM PATTERNS IN TEMPORAL-LOBE EPILEPSY PATIENTS

The usefulness of MEG-based techniques in lateralizing and localizing the epileptogenic area was investigated in the present study. Spontane ous and methohexital-induced spikes were studied in a group of 15 pati ents with temporomesial epilepsy using a 37-channel neuromagnetometer. The accuracy of the magnetic source imaging was compared to the resul ts of electrocorticographic (ECoG) recordings. Differences of drug-ind uced spike densities in the MEG recordings between both sides confirme d a similar lateralizing power of the MEG and ECoG recordings. Source location analyses based on a moving dipole model resp. a rotating dipo le model were performed using a spherical head model. After subdivisio n of the volume of each patient's head, 8 cm(3) cubicles containing at least 3 source locations were projected onto the individual MRI scan and resulted in source locations within or close to the presurgically defined primary epileptogenic area only in 3 of the 15 patients. Spike induction by methohexital has the advantage of shortening the recordi ng period as compared to recordings of interictal epileptiform dischar ges. However: the correlation analyses of spike densities from MEG and ECoG recordings and the source location analyses from MEG recordings indicate that spikes generated in deep temporomesial structures may es cape the MEG registration. (C) 1997 Elsevier Science Ireland Ltd.