Abstracts

Rationale: Spike and slow wave complexes are typical epileptic discharges in focal epilepsy. Such spikes are associated with high-frequency oscillations (HFOs) which are linked to epileptic excitation. The post-spike slow waves (PSS) relate to inhibitory activity. Preictal power imbalance between spike-related HFOs and PSS in the spike and slow wave complex is associated with seizure initiation. The aim of this study is to elucidate where and when this power imbalance occurs in patients with focal epilepsy.Methods: We retrospectively analyzed intracranial EEG data from six pediatric patients with focal cortical dysplasia type II, who underwent extraoperative video–EEG. In each patient, we carefully determined the seizure onset zone (SOZ) and irritative zone (IZ), and divided the preictal 3-min period into three intervals: 0-1 min, 1-2 min, and 2-3 min before seizure onset. In the respective zones and intervals, we calculated the power of spike-related HFOs with 80-200 Hz and PSS in the spike and slow wave complexes, and performed correlation (Spearman's coefficient) and simple linear regression analyses comparing HFO and PSS power. Across all patients, the Steel-Dwass test was used to verify the difference of slope of regression lines among three preictal 1-min intervals.Results: During 3-min preictal periods, positive correlation between HFO and PSS power was maintained in the IZ, but drastically reduced in the SOZ. The slope of regression line (ΔPSS/ΔHFO power) showed no significant differences among three preictal 1-min intervals in the IZ, but decreased significantly during 0-1 min before seizure onset (p < 0.05, Steel-Dwass test) in the SOZ.Conclusions: Dynamic preictal imbalance between HFO and PSS power selectively occurs in the SOZ. The collapse of excitation/inhibition balance in the SOZ is related to the focal ictogenesis. Our analysis and results will provide a potential biomarker to identify the SOZ and predict seizure occurrence in patients with focal epilepsy.