Frequency band coupling with high-frequency activities in tonic-clonic seizures shifts from θ to δ band

Objective: To clarify variations in the relationship between high-frequency activities (HFAs) and low-frequency bands from the tonic to the clonic phase in focal to bilateral tonic-clonic seizures (FBTCS), using phase-amplitude coupling. Methods: This retrospective study enrolled six patients with drug-resistant focal epilepsy who underwent intracranial electrode placement at Osaka University Hospital (July 2018-July 2019). We recorded 11 FBTCS. The synchronization index (SI) and receiver-operating characteristic (ROC) analysis were used to analyze the coupling between HFA amplitude (80-250 Hz) and lower frequencies phase. Results: In the tonic phase, the theta (4-8 Hz)-HFA coupling peaked, and the HFA power occurred at baseline (0 mu V) of theta oscillations. In contrast, in the clonic phase, the delta (2-4 Hz)-HFA coupling peaked, and the HFA power occurred at the trough of delta oscillations. ROC analysis indicated that the delta-HFA SI discriminated well the clonic from the tonic phase. Conclusions: The main low-frequency band modulating the HFA shifted from the theta band in the tonic phase to the delta band in the clonic phase. Significance: Neurophysiological key frequency bands were implied to be the theta band and delta band in tonic and clonic seizures, respectively, which improves our understanding of FBTCS. (C) 2022 International Federation of Clinical Neurophysiology. Published by Elsevier B.V.