Higher phase-amplitude coupling between ripple and slow oscillations indicates the distribution of epileptogenicity in temporal lobe epilepsy with hippocampal sclerosis

Abstract

Objective: We assessed the diagnostic utility of the occurrence rate of high-frequency oscillations and modulation index (MI) from intraoperative electrocorticography (ioECoG) in determining the extent of epileptogenicity in mesial temporal lobe epilepsy (TLE) with hippocampal sclerosis (HS).

Methods: We enrolled 17 patients who underwent selective amygdalohippocampectomy (SelAH) for TLE due to HS. We analyzed the occurrence rate of ripples (80-200 Hz) and fast ripples (200-300 Hz); and MI between ripples and 3-4 Hz (MI_{Ripples/3-4 Hz}) and fast ripples and 3-4 Hz (MI_{FRs/3-4 Hz}) from the amygdala, hippocampus, and lateral temporal lobe (LTL) pre-SelAH and the LTL post-SelAH, and subsequently categorized the patients into good and poor seizure outcome groups. We compared the occurrence rates and MIs over each region of interest between both groups. Receiver operating characteristic analysis was used to identify the most optimal indicator to predict poor surgical outcomes.

Results: In the poor seizure outcome group, an increase in the occurrence rate of ripples was seen in the hippocampus and LTL pre-SelAH and the LTL post-SelAH. The MI_{Ripples/3-4 Hz} from the LTL pre-SelAH was the most indicative factor of poor outcome.

Conclusions: High occurrence rate of ripples and MI_{Ripples/3-4 Hz} from the LTL showed wide epileptogenicity in TLE patients with poor seizure outcomes after SelAH. Our data suggest that the analysis of the occurrence rate of HFOs and MI_{HFOs/3-4 Hz} from ioECoG, especially from the LTL, can indicate the distribution of epileptogenicity in TLE with HS.

Keywords: Electrocorticography; High-frequency oscillation; Modulation index; Phase-amplitude coupling; Selective amygdalohippocampectomy; Temporal lobe epilepsy.