ELECTROCORTICOGRAPHY IN PATIENTS WITH MEDICALLY INTRACTABLE TEMPORAL-LOBE SEIZURES .1. QUANTIFICATION OF EPILEPTIFORM DISCHARGES PRIOR TO RESECTIVE SURGERY

We studied retrospectively the intraoperative preresection electrocort icograms (ECoGs) of 72 patients undergoing surgery for medically intra ctable, mostly complex partial, temporal lobe seizures (TLS). Quantifi cation of interictal epileptiform discharges (EDs) detected visually a t each electrode location in 2 min recording epochs included computati ons of ED rates (EDs/min) and cumulative voltages (CuVs) muV/min). Of 6388 EDs, 81% involved the infratemporal surface, 18% the lateral temp oral surface and 1% the orbital frontal area. Forty-eight patients (67 %) demonstrated multiple (up to 5 or more), temporally independent foc i. Dominant foci in medial and lateral infratemporal locations were ab out equally common and were significantly more frequent than in latera l temporal locations. Rankings of ED CuVs and rates at individual cort ical locations defined 4 areas of ''relative interictal cortical epile ptogenicity.'' These were arranged in an orderly pattern with the ante rior parahippocampal gyrus and the inferomedial surface of the tempora l tip displaying the highest and the lateral temporal and posterior in fratemporal cortices showing the lowest propensity to the interictal e pileptiform discharge. Individual areas were not characterized by dist inct clinical seizure manifestations, Preresection ECoGs provide infor mation on the epileptogenic dysfunction that involves most of the temp oral lobe of patients with medically intractable TLS.