REM sleep

The key brain structure for generating REM sleep is the brainstem, particularly the pons and adjacent portions of the midbrain. These areas and the hypothalamus contain cells that are maximally active in REM sleep, called REM-on cells, and cells that are minimally active in REM sleep, called REM-off cells. Subgroups of REM-on cells use the transmitter gammaaminobutyric acid (GABA), acetylcholine, glutamate, or glycine. Subgroups of REM-off cells use the transmitter norepinephrine, epinephrine, serotonin, histamine, or GABA. Lesions of several regions in the pons and medulla can cause REM sleep to occur without the normal loss of muscle tone. Stimulation of portions of the REM sleep-controlling area of the pons can produce a loss of muscle tone in antigravity and respiratory musculature, even without eliciting all aspects of REM sleep. Most cases of human narcolepsy are caused by a loss of hypocretin (orexin) neurons.