Abstracts

Rationale: Temporal lobe seizures are frequently encountered in patients with medically intractable epilepsy requiring surgical intervention. Interactions between temporal neocortex and medial temporal lobe are complex and may be responsible for inhibiting or facilitating the onset of seizures.Methods: Patients who fulfilled following criteria were include in the study. 1) suffered medically intractable epilepsy, 2)underwent two-stage epilepsy surgery, 3) intraoperative ECoG recorded following implantation of the electrode during the first surgery, 4)invasive EEG monitoring included temporal neocortical and medial temporal coverage, 5) epileptogenic zone involved the temporal lobe, 6) post-resection ECoG was recorded during the second surgery. During temporal lobectomy, the lateral temporal lobe was resected en bloc and temporal horn was opened. A four contact subdural electrode strip with inter-electrode distance of 1 cm was placed over the ventricular hippocampal surface. The electrode # 1 was placed most posterirorly (over the tail of hippocampus) and electrode # 4 was over the head of the hippocampus. A minimum of 10 minute ECoG sample was acquired digitally with sampling rate of 200 Hz. The ECoG was analyzed with reformated refrential and bipolar montages utilizing band pass filter of 1-70 Hz.Results: Total of seven patients fulfilled the criteria. All but one had left temporal lobectomy. Immediate post-implantation ECoG recorded during the first stage of surgery did not reveal electrographic seizure in any patient. During extra-operative intracranial EEG monitoring, all patients had all or some of the seizures originating from the hippocampus. Five of the seven hippocampal ECoG recording following temporal resection revealed electrographic seizure. All seizures recorded from contacts 2 or 3 located over the body of the hippocampus.Conclusions: Removal of the temporal neocortex leads to exacerbation of electrographic seizures in the hippocampus acutely. Temporal neocortex probably provides inhibitory control over the medial temporal lobe structures in patients with medial temporal lobe seizures.