Original articleFast (40-150Â Hz) oscillations are associated with positive slow waves in the ictal EEGs of epileptic spasms in West syndrome

ObjectiveTo elucidate the generative mechanisms of epileptic spasms (ESs) in West syndrome, we investigated the temporal relationship between scalp fast (40-150 Hz) oscillations (FOs) and slow waves in the ictal electroencephalograms (EEGs) of ESs.MethodsIn 11 infants with WS, ictal FOs were detected in a bipolar montage based on spectral and waveform criteria. Their temporal distribution was analyzed in terms of the positive peaks (trough point, TT) of identical EEG data in a referential montage. Among six EEG data sections defined according to TT, the number of FOs, peak power values, and peak frequencies were compared.ResultsWe identified a total of 1014 FOs (946 gamma and 68 ripple oscillations), which clustered closely at TT. The number of gamma oscillations in the 1 s epoch including TT was significantly higher than those in the prior and subsequent phases. Peak power values and frequencies tended to be higher in these positive phase sections.ConclusionsThe temporal association of FO clustering and positive slow waves in the ictal EEGs of ES indicated that active neuronal firing related to FOs underlies the generation of ESs and their ictal slow waves.