Rapid eye movement sleep is a unique phase of sleep in mammals and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream vividly.
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REM sleep is physiologically different from the other phases of sleep, which are collectively referred to as non-REM sleep.
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The transition to REM sleep brings marked physical changes, beginning with electrical bursts called "ponto-geniculo-occipital waves" originating in the brain stem.
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Organisms in REM sleep suspend central homeostasis, allowing large fluctuations in respiration, thermoregulation and circulation which do not occur in any other modes of sleeping or waking.
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REM sleep was further described by researchers, including William Dement and Michel Jouvet.
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REM sleep is coined "paradoxical" because of its similarities to wakefulness.
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Brain energy use in REM sleep, as measured by oxygen and glucose metabolism, equals or exceeds energy use in waking.
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Neural activity during REM sleep seems to originate in the brain stem, especially the pontine tegmentum and locus coeruleus.
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REM sleep is punctuated and immediately preceded by PGO waves, bursts of electrical activity originating in the brain stem.
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The areas activated during REM sleep are approximately inverse to those activated during non-REM sleep and display greater activity than in quiet waking.
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Whereas acetylcholine manifests in the cortex equally during wakefulness and REM sleep, it appears in higher concentrations in the brain stem during REM sleep.
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An alternative explanation suggests that the functional purpose of REM sleep is for procedural memory processing, and the rapid eye movement is only a side effect of the brain processing the eye-related procedural memory.
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Patients with suspected REM sleep disorders are typically evaluated by polysomnogram.
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Rapid eye movement sleep has since its discovery been closely associated with dreaming.
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Sleepers awakened from REM tend to give longer, more narrative descriptions of the dreams they were experiencing, and to estimate the duration of their dreams as longer.
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However, people woken up during sleep do not report significantly more bizarre dreams during phasic REMS, compared to tonic REMS.
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Certain scientific efforts to assess the uniquely bizarre nature of dreams experienced while aREM sleep were forced to conclude that waking thought could be just as bizarre, especially in conditions of sensory deprivation.
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The prospect that well-known neurological aspects of REM sleep do not themselves cause dreaming suggests the need to re-examine the neurobiology of dreaming per se.
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However, the subjective intensity of dreaming increased and the proclivity to enter REM sleep was decreased during SSRI treatment compared to baseline and discontinuation days.
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People awakened from REM sleep have performed better on tasks like anagrams and creative problem solving.
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The first REM episode occurs about 70 minutes after falling asleep.
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Tonic REM sleep is characterized by theta rhythms in the brain; phasic REM sleep is characterized by PGO waves and actual "rapid" eye movements.
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Whether and how long-term REM sleep deprivation has psychological effects remains a matter of controversy.
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Antidepressants and stimulants interfere with REM sleep by stimulating the monoamine neurotransmitters which must be suppressed for REM sleep to occur.
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The primary criteria used to identify REM sleep are the change in electrical activity, measured by EEG, and loss of muscle tone, interspersed with bouts of twitching in phasic REM sleep.
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Some researchers argue that the perpetuation of a complex brain process such as REM sleep indicates that it serves an important function for the survival of mammalian and avian species.
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In both humans and experimental animals, REM sleep loss leads to several behavioral and physiological abnormalities.
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Loss of REM sleep has been noticed during various natural and experimental infections.
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Survivability of the experimental animals decreases when REM sleep is totally attenuated during infection; this leads to the possibility that the quality and quantity of REM sleep is generally essential for normal body physiology.
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In rats, REM sleep increases following intensive learning, especially several hours after, and sometimes for multiple nights.
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Artificial enhancement of the non-REM sleep improves the next-day recall of memorized pairs of words.
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Graeme Mitchison and Francis Crick proposed in 1983 that by virtue of its inherent spontaneous activity, the function of REM sleep "is to remove certain undesirable modes of interaction in networks of cells in the cerebral cortex"—a process they characterize as "unlearning".
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Memory consolidation during paradoxical REM sleep is specifically correlated with the periods of rapid eye movement, which do not occur continuously.
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REM sleep could provide a unique opportunity for "unlearning" to occur in the basic neural networks involved in homeostasis, which are protected from this "synaptic downscaling" effect during deep sleep.
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Ioannis Tsoukalas of Stockholm University has hypothesized that REM sleep is an evolutionary transformation of a well-known defensive mechanism, the tonic immobility reflex.
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Dr David M Maurice, an eye specialist and former adjunct professor at Columbia University, proposed that REM sleep was associated with oxygen supply to the cornea, and that aqueous humor, the liquid between cornea and iris, was stagnant if not stirred.
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However, owls experience REM sleep, but do not move their head more than in non-REM sleep and is well known that owls' eyes are nearly immobile.
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