Cortical and subcortical EEG in relation to sleep-wake behavior in mammalian species

In humans and several other mammals, a quantitative EEG analysis has been used to study the regulation of sleep-wake behavior. In all mammalian species studied, cortical EEG recorded during non-REM sleep (NREMS) is characterized by the occurrence of spindles and high voltage, slow waves (0.5-4.0 Hz). Furthermore, slow-wave activity (SWA) is low at the beginning of a NREM episode and it rises in the course of a NREM episode. The rise rate and the maximal level of SWA are a monotonic function of the duration of prior wakefulness. During REMS, cortical EEG typically exists of low-voltage, mixed frequencies and. in some animals, a prominent theta rhythm is superimposed. Only after sleep deprivation in some species does cortical EEG within REMS change. Especially, the EEG activity during wakefulness depends considerably on the behavioral state, on the electrode location and on the species. On average, cortical EEG within wakefulness consists of low-voltage, mixed frequencies. The few studies done on subcortical EEG clearly show that the electrical activity differs highly between brain regions and between species. However, two recent studies, in which a spectral analysis of subcortical EEG was made, showed that, at least in humans and cats, the changes occurring in subcortical EEG associated with changes in sleep-wake behavior parallel the general characteristics of cortical EEG described above.