High and low frequency oscillations in epileptic seizures

Objectives: The correlation between the amplitude of higher frequency component (30–150 Hz) and phase of lower frequency component interacts to brain activities. This phenomenon is called phase-amplitude coupling (PAC) and it may play an important role within brain for information processing. We hypothesizes that alternation of PAC would correlate epileptic attacks.

Method: We included 7 patients who had diagnosed as lateral temporal epilepsy with non-invasive studies. The video-electroencephalography with chronic intracranial electrodes (V-iEEG) was performed in all 7 patients. V-iEEG was recorded for 7–14 days continually including ictal and inter-ictal periods with the sample rate of 10,000 Hz. PAC, that is between the phase of low frequency components (theta, alpha, beta: 4–30 Hz) and the amplitude of high frequency components (high-gamma: 80–130 Hz), was analyzed using MATLAB (ver.2013b). The strength of PAC was computed as synchronization index (SI). Mean SI in every 1 min was shown serially during the long-term examination including both ictal and inter-ictal periods.

Result: Although SI scores were stable during inter-ictal period, significantly higher SI scores were observed during peri-ictal periods compared to inter-ictal periods.

Conclusion: Alteration of CFC should correlate the epileptic attack in patients with lateral temporal epilepsy. We conclude that CFC might be a parameter of prediction of epileptic seizure and that it would contribute to investigate the pathology of epilepsy.