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

ObjectiveTo 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. MethodsThis retrospective study enrolled six patients with drug-resistant focal epilepsy who underwent intracranial electrode placement for presurgical invasive electroencephalography at Osaka University Hospital (July 2018-July 2019). We used intracranial electrodes to record seizures in focal epilepsy (11 FBTCS). The magnitude of synchronization index (SIm) and receiver-operating characteristic (ROC) analysis were used to analyze the coupling between HFA amplitude (80-250 Hz) and lower frequencies phase. ResultsThe {theta} (4-8 Hz)-HFA SIm peaked in the tonic phase, whereas the {delta} (2-4 Hz)-HFA SIm peaked in the clonic phase. ROC analysis indicated that the {delta}-HFA SIm discriminated well the clonic from the tonic phase. ConclusionsThe main low-frequency band modulating the HFA shifted from the {theta} band in the tonic phase to the {delta} band in the clonic phase. SignificanceIn FBTCS, low-frequency band coupling with HFA amplitude varies temporally. Especially, the {delta} band is specific to the clonic phase. These results suggest dynamically neurophysiological changes in the thalamus or basal ganglia throughout FBTCS. HighlightsO_LIThe {theta} band (4-8 Hz) was mainly coupled with high-frequency activity (HFA) in the tonic phase of focal to bilateral tonic-clonic seizures (FBTCS). C_LIO_LIThe {delta} band (2-4 Hz) was mainly coupled with HFA in the clonic phase of FBTCS. C_LIO_LIThe magnitude of the synchronization index related to {delta}-HFA phase-amplitude coupling discriminated well the clonic from the tonic phase. C_LI