Phase-amplitude coupling of ripple activities during seizure evolution with theta phase

Objective: High-frequency activities (HFAs) and phase-amplitude coupling (PAC) are key neurophysiological biomarkers for studying human epilepsy. We aimed to clarify and visualize how HFAs are modulated by the phase of low-frequency bands during seizures. Methods: We used intracranial electrodes to record seizures of focal epilepsy (12 focal-to-bilateral tonicclonic seizures and three focal-aware seizures in seven patients). The synchronization index, representing PAC, was used to analyze the coupling between the amplitude of ripples (80-250 Hz) and the phase of lower frequencies. We created a video in which the intracranial electrode contacts were scaled linearly to the power changes of ripple. Results: The main low frequency band modulating ictal-ripple activities was the 0 band (4-8 Hz), and after completion of ictal-ripple burst, d (1-4 Hz)-ripple PAC occurred. The ripple power increased simultaneously with rhythmic fluctuations from the seizure onset zone, and spread to other regions. Conclusions: Ripple activities during seizure evolution were modulated by the 0 phase. The PAC phenomenon was visualized as rhythmic fluctuations. Significance: Ripple power associated with seizure evolution increased and spread with fluctuations. The 0 oscillations related to the fluctuations might represent the common neurophysiological processing involved in seizure generation. (c) 2021 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.