Dopamine neurons in the ventral tegmental area modulate REM sleep

identified periods of 'active sleep' that are marked by rapid-eye-movements that alternate with 'quiescent sleep' periods in human infants. Several years later Dement and Kleitman showed that rapid-eye-movements are correlated with specific patterns of brainwave activity and that vivid dreaming occurs during periods of rapid-eye-movements in human adults. Shortly thereafter, Jouvet identified a similar behavioural state in cats, showing that cats also experience periods of rapid-eye-movements that occur during periods of muscle atonia and wake-like cortical activity. REM sleep, or REM sleep-like states, have subsequently been identified in a variety of animals, including marsupials, birds, fish, insects, octopi, and lizards. These observations suggest that REM sleep is conserved across the animal kingdom and imply that REM sleep plays a role in normal biology and physiology. Although REM sleep was initially characterized by rapid-eye-movements, we now know that it is also characterized by a range of physiological features, including reduced amplitude and faster frequency cortical electroencephalogram (EEG) that is reminiscent of waking, high-amplitude theta waves in the hippocampus, active suppression of skeletal muscle activity (i.e., REM atonia), intermittent muscle twitches, autonomic and respiratory activation, fluctuations in