Abstracts

Rationale: Fast oscillations (FOs) were firstly explored from scalp electroencephalogram (EEG) data of hypsarrhythmia in West syndrome (infantile spasms) to investigate the meaning of FOs in this epileptic encephalopathy.Methods: In 17 infants with West syndrome, we conservatively detected fast frequency peaks that stood out from the time-frequency spectral background with square-root power > 1 µV (spectral criterion) and corresponded to clear FOs with at least four oscillations in the filtered EEG traces (waveform criterion) in sleep EEGs.Results: We found a total of 1519 interictal FOs that fulfilled both the spectral and waveform criteria. The FOs with a median frequency of 56.6 Hz (range 41.0 - 140.6 Hz) were dense, with a median rate of 66 (24 - 171) per min before ACTH treatment, which was significantly higher than that in control infants without seizures (median 1; p < 0.001). The FOs were reduced by treatment. The mean gamma and ripple oscillation rates that were detected using the waveform criterion alone were 40.62/min and 15.75/min, respectively, per channel: these results were 112.8 and 98.4 times higher, respectively, than the previously reported corresponding rates in adult epilepsy patients.Conclusions: The observed FOs corresponded to epileptogenicity because of their close relation to the severity of hypsarrhythmia during the course of ACTH treatment. The very high epileptic FO rates in hypsarrhythmia are thought to affect the process of neuro-development by interfering with physiological functions in West syndrome, taking into account that high frequencies are also important in physiological higher brain functions.