Functionality of Sleep

NEUROSCIENCE: SLEEP AND THE BRAIN: "the brain is relatively quiescent during slow-wave sleep (when the EEG is dominated by sleep spindles and high-voltage slow waves). But it must be emphasized that such global deactivation is only relative. Although consciousness is dulled, the brain is still roughly 80% activated and thus capable of robust and elaborate information processing. Thus, the EEG spindles and slow waves represent changes in the excitability of cortical and thalamic circuitry and should be regarded not simply as 'noise', which subjective experience leads us to assume, but as signals used by the brain for its own functional purposes."