Spatiotemporal Brain Dynamics During Cyclic Seizures of Super-Refractory Status Epilepticus

Cyclic seizures (CS) are defined by the periodic recurrence of epileptic activity and may offer critical insights into the mechanisms of seizure termination. Previous studies have reported increased network synchronization during the final stages of seizures. The objective of this study was to investigate hypersynchronization at the termination of cyclic seizures and to characterize its spatial distribution.

To quantify brain synchronization, we calculated the imaginary coherence in a low-frequency band (LF-iCOH) at different ictal phases. Synchronization was calculated at both scalp regions and electrode levels. A total of 10 patients were selected, and 1230 seizures from 468 h of EEG monitoring were analyzed.

Eight patients exhibited a significant increase in LF-iCOH at seizure termination in both regional and electrode-level analyses, with varying topographies. Hypersynchronization at the end of seizures was predominantly observed in the anterior and centrotemporal regions compared to the posterior regions.

Terminal hypersynchronization was observed in all patients with focal to bilateral seizures and one patient with focal seizures, and was not observed in patients with localized focal seizures. The diverse topographies of terminal hypersynchronization observed suggest that this process is not related to any specific scalp area or seizure onset zone. These results suggest a common mechanism of seizure termination in the continuum of single seizures to the most severe form of SE.