Human sleep EEG oscillations and their neurophysiological significance

We have reported three sleep electroencephalogram (EEG) frequencies whose fast Fourier transform (FFT) power show rhythmic fluctuations throughout the night; Delta (0.3-3 Hz), sigma (12-16 Hz) and beta (20-28 Hz). We investigated these frequencies using conventional polysomnography (PSG), EEG topography and electrocorticography (ECoG). Polysomnography was useful for extracting the dynamic changes of these three EEG frequencies throughout the night. Topographies revealed different distributions of each frequency on the skull. ECoG was applied to study the sigma frequency, which was not apparent on the temporal cortex. The absence of the sigma frequency may indicate that the temporal cortex does not receive influences from the reticular nucleus of the thalamus, which is considered to be the generator of sigma spindles. These results indicate that multimodal studies of these frequencies can shed light on both our knowledge of sleep and brain structure.