Identification of the epileptogenic zone using phase–amplitude coupling on ictal electroencephalography: authentic or spurious PAC?

Abstract

Objective: Phase-amplitude coupling (PAC) can arise from actual relations betweenoscillations at different frequencies (authentic PAC) or from harmonic effects (spurious PAC).To assess the importance of these PAC mechanisms, we investigated the modulation index(MI) and time locked index (TLI) between epileptogenic zone (EZ) and non-EZ groups duringseizures.Methods: We analyzed 34 patients with drug-resistant epilepsy who underwentstereoelectroencephalography (SEEG) implantation. SEEG data was classified into threeperiods: “preictal,” “fast,” and “rhythmic.” The amplitude of ripple bands (80–200 Hz) andthe phase of three slow wave bands (α, β, and θ band) were used for MI and TLI. The capacityof MI to detect the EZ was tested with precision and recall measures, summarized by F1score.Results: The MI was significantly greater in EZ group than that in non-EZ group for allperiods. The best F1 results were obtained for the “fast” period. Both authentic and spuriousPAC were present during all periods and bands.Conclusions: Different PAC mechanisms could be observed during different seizure periods.Care should be taken when interpreting MI as a measure of authentic PAC.Significance: A combination of MI and TLI can help the interpretation of ictal crossfrequency observations.