Abstracts

Rationale: In the presurgical evaluation of drug-resistant epilepsy patients high-frequency oscillations (HFOs) recorded by intracranial electrode recordings are previously reported as a markers of epileptogenicity. But we often find it difficult to isolate pathological HFOs in the epileptogenic tissue from the physiological HFOs in the normal tissue or functional cortex. The anesthetic agent affects the occurrence of HFOs in intraoperative ECoG. We studied the effect of propofol administration on the occurrence of pathological HFOs and physiological HFOs. Methods: The subjects comprised of 11 patients (mean age 25.3 years and ranged 10–57 years; 8 males) with drug-resistant epilepsy who underwent extra-operative intracranial electroencephalography (EEG) monitoring for surgical treatment of epilepsy. Implanted electrodes were consisted of depth electrodes (median, 6 contacts per patient; range, 0–26 contacts) and subdural electrodes (median, 44 contacts per patient; range, 23–108 contacts). All patients underwent surgical resection and six achieved freedom from seizures postoperatively. Intracranial EEG signals were sampled and recorded at 1000 Hz simultaneously with scalp EEG and electromyography for sleep staging.The recorded signals were filtered between 80 and 200 Hz, and interictal ripples were automatically detected on 2-5 min EEG samples derived from anesthesia with propofol and NREM sleep. Ripples were defined by events above five times the standard deviation of baseline activities and containing at least four consecutive oscillations. The definition of “seizure onset zone (SOZ)” electrode was as below; ictal activity began from the electrode in ictal video-EEG recording and the surgical resection involving the electrode resulted the patient seizure freedom. The functional areas of primary motor, primary sensory, visual and language cortex were defined if the neurological symptoms were elicited by the direct cortical stimulation of the electrodes. The occurrence rate of ripples was compared between the state under propofol administration and NREM sleep. Results: The occurrence rate of ripples under the propofol administration and NREM sleep was mean 11.12/min,10.10/min (n=31) in SOZ, mean 0.73/min, 0.30/min (n=9) in primary motor cortex, mean 2.59/min, 0.47/min (n=19) in primary sensory cortex, mean 6.77/min, 8.56/min (n=14) in visual cortex, mean 0.86/min, 0.30/min (n=10) in language cortex respectively. The occurrence rate of ripples in SOZ was significantly higher than functional areas except for visual cortex in both condition of propofol administration and NREM sleep (p < 0.05, Wilcoxon test). Conclusions: The tendency of occurrence rates of ripples in SOZ and functional areas was less influenced under anesthesia with propofol. Pathological HFOs occur more frequently than physiological HFOs in functional areas except for visual cortex. There was no significant difference on the occurrence of HFOs between propofol administration and NREM sleep. Funding: None