Basic mechanisms of sleep generation.

Most brainstem, thalamic, and cortical cellular types undergo similar processes during rapid eye movement (REM) sleep and wakefulness, and both these brain-activated behavioral states are opposed to the resting EEG-synchronized sleep. Experimental evidence shows that during drowsiness, disfacilitation in thalamic and cortical neurons (by partial removal of influences from mesopontine, posterior hypothalamic, and basal forebrain activating systems) may coexist with active hypnogenic mechanisms. The idea of an active induction of sleep, however, still lacks firm support at the cellular level. The generation of REM sleep signs is probably caused, at least partially, by the disinhibition of mesopontine cholinergic cells, the executive elements of tonic and phasic events during dreaming sleep, following cessation of firing of inhibitory serotonergic dorsal raphe neurons.