Abstracts

Rationale: In order to attain a good seizure control by epilepsy surgery, it is important to detect epileptic focus precisely. Chronic Video-intracranial EEG (iEEG) monitoring with subdural electrodes and depth electrodes have been applied for this purpose in selected patients. Recently, iEEG activities in the higher (≥150 Hz) than gamma range has been observed during interictal and ictal phases, and considered as pathological phenomenon related to epileptgenecity. Moreover, it is reported that some rhythmic neural activities with different frequencies occur with certain correlation and those have been observed in hippocampus or visual cortex. This phenomenon is called cross-frequency-coupling (CFC) and it attracts attention as the important side of the information processing within a brain.In this study, we investigated the CFC between the iEEG activities in high gamma and lower basic frequencies in peri-ictal phase. Methods: The iEEG data of 9 patients with intractable epilepsy from January 2013 to May 2014 were studied. Sampling rates of V-iEEG was 10000 Hz. Analysis of CFC was performed by using MATLAB (ver.2013b).That CFC between the phase of low frequency wave (theta, alpha, beta: 4 to 30 Hz) and the amplitude of high frequency wave (high-gamma wave: 80 to 130 Hz) was calculated in all electrodes.The strength of CFC was computed as Synchronization Index (SI). Mean SI in every 1 minute was calculated serially around ictal onset. Results: Total 10 ictal iEEG in 7 patients were studied, and high SI (more than twofold average SI at rest) during peri-ictal phase were observed in all of them. Those high SI were seen around the clinical diagnosed ictal onset zone. Especially, in 4 ictal iEEG in 3 patients, the SI was gradually increased about 5-10 minutes before and showed its peak at ictal onset. Conclusions: We found the local alteration of CFC between low frequency phase and high gamma amplitude in iEEG from pre-ictal to ictal onset. According to these results, we considered that CFC can become a parameter of epileptic seizure prediction about the onset time.