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

Abstract

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 θ (4-8 Hz)-HFA coupling peaked, and the HFA power occurred at baseline (0 μV) of θ oscillations. In contrast, in the clonic phase, the δ (2-4 Hz)-HFA coupling peaked, and the HFA power occurred at the trough of δ oscillations. ROC analysis indicated that the δ-HFA SI discriminated well the clonic from the tonic phase.

Conclusions: The main low-frequency band modulating the HFA shifted from the θ band in the tonic phase to the δ band in the clonic phase.

Significance: Neurophysiological key frequency bands were implied to be the θ band and δ band in tonic and clonic seizures, respectively, which improves our understanding of FBTCS.

Keywords: Delta band; Focal to bilateral tonic-clonic seizures; High-frequency activities; Intracranial EEG; Phase-amplitude coupling; Theta band.