ELECTROCORTICOGRAPHY IN PATIENTS WITH MEDICALLY INTRACTABLE TEMPORAL-LOBE SEIZURES .2. QUANTIFICATION OF EPILEPTIFORM DISCHARGES FOLLOWING SUCCESSIVE STAGES OF RESECTIVE SURGERY

We quantified retrospectively the interictal epileptiform discharges ( EDs) detected visually in the electrocorticograms (ECoGs) of 42 patien ts undergoing successive stages of anterior temporal lobectomy for med ically intractable temporal lobe seizures (TLS). Following first resec tion sparing the hippocampus (H) and the parahippocampal gyrus (PHG), EDs were recorded on both structures in all patients and by far exceed ed in amount those on residual lateral infratemporal and lateral tempo ral cortices. Frequently, EDs occurred apparently simultaneously but w ith opposite polarities on the H and the PHG, but more complex relatio nships were also evident in most individuals. These features likely re flected abnormal post-synaptic activity generated at different locatio ns and cortical depths within the H, PHG, or both. Quantification of e pileptiform activity and the effects of selective anterior hippocampec tomy or parahippocampectomy suggested that both the H and PHG had rema rkable epileptogenic potential. Levels of epileptiform activity were n ot significantly different in the H and PHG and in the H of subjects w ith and without H sclerosis. After final resection, including the amyg daloid nucleus (AN), anterior H and PHG, interictal EDs were present, although markedly diminished, in 35 patients. Postresection foci were significantly less numerous and extensive, and attained smaller Maxima l voltages, than did foci before and after first resection.