Rapid eye movement sleep
REM sleep is a paradoxical phase of sleep linked to dreaming.
Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in all mammals and birds, as well as in some reptiles. It is defined by the random rapid movement of the eyes, low muscle tone throughout the body, and a strong tendency for the sleeper to experience vivid dreams. During this phase, core body and brain temperatures rise, while skin temperature drops to its lowest point. REM sleep is also called paradoxical sleep because its brain activity—fast, low-voltage, desynchronized waves—closely resembles that of wakefulness, even as the body remains largely paralyzed. The electrical and chemical regulation of this phase originates in the brain stem, marked by high levels of the neurotransmitter acetylcholine and an almost complete absence of the monoamine neurotransmitters histamine, serotonin, and norepinephrine. The lack of norepinephrine prevents experiences during REM sleep from being transferred into permanent memory. REM sleep alternates with non-REM sleep within a sleep cycle lasting about 90 minutes in adult humans, and as the night progresses, cycles shift toward more REM sleep. The transition into REM begins with electrical bursts called ponto-geniculo-occipital (PGO) waves from the brain stem. During REM sleep, the body suspends central homeostasis, allowing large fluctuations in respiration, thermoregulation, and circulation that do not occur in other sleep or waking states. Muscle tone is abruptly lost in a state known as REM atonia. In 1953, Professor Nathaniel Kleitman and his student Eugene Aserinsky identified rapid eye movement and linked it to dreaming. Subsequent research by William Dement and Michel Jouvet further characterized this phase. Experiments involving REM deprivation, where subjects are awakened at the onset of REM, typically lead to a modest REM rebound when they are allowed to sleep normally again.
- field
- Sleep physiology and neuroscience
- known_for
- Phase of sleep associated with vivid dreaming, rapid eye movements, and brain activity resembling wakefulness
- key_researchers
- Nathaniel Kleitman, Eugene Aserinsky, William Dement, Michel Jouvet
Lore & Background
Rapid eye movement sleep, also known as paradoxical or desynchronized sleep, is a distinct phase occurring in all mammals, birds, and some reptiles. It is defined by the random, rapid movement of the eyes, a near-total loss of muscle tone (REM atonia), and a high likelihood of vivid dreaming. During this phase, core body and brain temperatures rise while skin temperature drops to its lowest point. The brain’s electrical activity becomes fast, low-voltage, and desynchronized, resembling wakefulness, with prominent theta rhythms in the hippocampus and gamma waves in the cortex. This contrasts sharply with the slow delta waves of deep non-REM sleep. Energy use in the brain during REM sleep matches or exceeds that of waking, while non-REM sleep uses 11–40% less. The phase is regulated by the brain stem, particularly the pontine tegmentum and locus coeruleus, and is marked by bursts of electrical activity called ponto-geniculo-occipital (PGO) waves, which originate in the brain stem and are linked to the rapid eye movements. Chemically, REM sleep features high levels of acetylcholine and a near absence of monoamines like histamine, serotonin, and norepinephrine; the lack of norepinephrine prevents the transfer of REM experiences into permanent memory. The body suspends central homeostasis during this phase, allowing large fluctuations in respiration, thermoregulation, and circulation. In adult humans, REM and non-REM sleep alternate in cycles lasting about 90 minutes, with REM periods becoming longer as the night progresses. Sensory deprivation during REM can lead to hallucinations.
Reader's Guide
REM sleep is physiologically distinct from non-REM sleep, alternating within a sleep cycle that lasts about 90 minutes in adult humans. As sleep cycles continue, the proportion of REM sleep increases. The transition to REM is marked by ponto-geniculo-occipital (PGO) waves from the brain stem, which precede rapid eye movements. During REM, the body loses muscle tone (REM atonia), and central homeostasis is suspended, allowing large fluctuations in respiration, thermoregulation, and circulation. Brain energy use in REM equals or exceeds that of waking, while non-REM sleep uses 11–40% less. The brain stem, particularly the pontine tegmentum and locus coeruleus, is the origin of neural activity during REM. Forebrain areas such as the limbic and paralimbic systems show heightened activation, linked to emotion, memory, fear, and sex. Chemically, REM involves high acetylcholine and near-absence of monoamine neurotransmitters norepinephrine, serotonin, and histamine. The absence of norepinephrine prevents transfer of REM experiences to permanent memory. The activation-synthesis hypothesis by Robert McCarley and Allan Hobson proposed that REM-on and REM-off neurons in the brain stem regulate the cycling between REM and non-REM sleep.
Did You Know?
- REM sleep is also called paradoxical sleep because the brain acts as if awake while the body is paralyzed.
- The core body and brain temperatures increase during REM sleep, while skin temperature decreases to its lowest values.
- REM sleep occurs about 4 times in a 7-hour sleep period.
- Injections of acetylcholinesterase inhibitor, which increases available acetylcholine, can induce paradoxical sleep in humans already in slow-wave sleep.
Frequently Asked Questions
Who is Rapid eye movement sleep?
REM sleep is a distinct stage of the sleep cycle found across mammals, birds, and certain reptiles, marked by quick darting of the eyes behind closed lids and a near-complete loss of muscle tone. It was first identified in the 1950s by researchers Nathaniel Kleitman and Eugene Aserinsky, with further groundwork laid by William Dement and Michel Jouvet.
What are Rapid eye movement sleep's powers/role?
During this phase, the brain fires off fast, low-voltage electrical patterns that look almost identical to wakefulness, while the body stays in a state of temporary paralysis. This paradoxical combination is where the most vivid, narrative-style dreams occur, and it plays a key role in consolidating memories and regulating brain chemistry.
How does Rapid eye movement sleep's story end?
Each REM episode typically lasts anywhere from ten to thirty minutes before the sleeper drifts back into deeper non-REM stages, and this cycle repeats roughly four to six times across a full night. The final REM period of the night tends to be the longest, often stretching well past thirty minutes before morning wakefulness.
Why is Rapid eye movement sleep important?
Without this phase, the brain loses a critical window for processing emotional experiences, strengthening learning, and resetting neurotransmitter balances. Researchers treat REM sleep as an essential tool for understanding how dreams form, how memory is organized, and how the nervous system maintains its day-to-day equilibrium.
What makes Rapid eye movement sleep 'paradoxical'?
The brain behaves as if the animal is fully awake—showing rapid, desynchronized electrical activity—yet the skeletal muscles are effectively switched off by inhibitory signals from the brainstem. This simultaneous wake-like brain activity and sleep-like muscular stillness is what earned the phase its nickname, paradoxical sleep.
More in Animal Biology And Behavior 1-21
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record