Rapid eye movement sleep
Techniques of neurosurgery, chemical injection, electroencephalography, positron emission tomography, and reports of dreamers upon waking have all been used to study this phase of sleep.
REM sleep is punctuated and immediately preceded by PGO (ponto-geniculo-occipital) waves, bursts of electrical activity originating in the brain stem.
[10] They exhibit their highest amplitude upon moving into the visual cortex and are a cause of the "rapid eye movements" in paradoxical sleep.
[19] Research in the 1990s using positron emission tomography (PET) confirmed the role of the brain stem and suggested that, within the forebrain, the limbic and paralimbic systems showed more activation than other areas.
[3][26] Unlike the abrupt transitions in electrical patterns, the chemical changes in the brain show continuous periodic oscillation.
[27] According to the activation-synthesis hypothesis proposed by Robert McCarley and Allan Hobson in 1975–1977, control over REM sleep involves pathways of "REM-on" and "REM-off" neurons in the brain stem.
In females, erection of the clitoris (nocturnal clitoral tumescence or NCT) causes enlargement, with accompanying vaginal blood flow and transudation (i.e. lubrication).
)[16] The mental events which occur during REM most commonly have dream hallmarks including narrative structure, convincingness (e.g., experiential resemblance to waking life), and incorporation of instinctual themes.
[45] Hobson and McCarley proposed that the PGO waves characteristic of "phasic" REM might supply the visual cortex and forebrain with electrical excitement which amplifies the hallucinatory aspects of dreaming.
[43] Another possible relationship between the two phenomena could be that the higher threshold for sensory interruption during REM sleep allows the brain to travel further along unrealistic and peculiar trains of thought.
[16][35]: 104 Previous research has shown that selective serotonin reuptake inhibitors (SSRIs) have an important effect on REM sleep neurobiology and dreaming.
[48] However, the subjective intensity of dreaming increased[48] and the proclivity to enter REM sleep was decreased during SSRI treatment compared to baseline and discontinuation days.
REM sleep through this process adds creativity by allowing "neocortical structures to reorganise associative hierarchies, in which information from the hippocampus would be reinterpreted in relation to previous semantic representations or nodes.
Sleep happens in the context of the larger circadian rhythm, which influences sleepiness and physiological factors based on timekeepers within the body.
Many animals and some people tend to wake, or experience a period of very light sleep, for a short time immediately after a bout of REM.
[55] After the deprivation is complete, mild psychological disturbances, such as anxiety, irritability, hallucinations, and difficulty concentrating may develop and appetite may increase.
[56] It has been suggested that acute REM sleep deprivation can improve certain types of depression—when depression appears to be related to an imbalance of certain neurotransmitters.
[69] A recent study found periodic eye movements in the central bearded dragon of Australia, leading its authors to speculate that the common ancestor of amniotes may therefore have manifested some precursor to REMS.
The "flower pot" method involves placing a laboratory animal above water on a platform so small that it falls off upon losing muscle tone.
The naturally rude awakening which results may elicit changes in the organism which necessarily exceed the simple absence of a sleep phase.
[56] Another method involves computer monitoring of brain waves, complete with automatic mechanized shaking of the cage when the test animal drifts into REM sleep.
[72] 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.
It fulfills important physiological needs vital for survival to the extent that prolonged REM sleep deprivation leads to death in experimental animals.
Experimental REM sleep deprivation has sometimes inhibited memory consolidation, especially regarding complex processes (e.g., how to escape from an elaborate maze).
[49]: 686 In humans, the best evidence for REM's improvement of memory pertains to learning of procedures—new ways of moving the body (such as trampoline jumping), and new techniques of problem solving.
[74] Tucker et al. demonstrated that a daytime nap containing solely non-REM sleep enhances declarative memory—but not procedural memory.
[66] 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".
[57] Ioannis Tsoukalas of Stockholm University has hypothesized that REM sleep is an evolutionary transformation of a well-known defensive mechanism, the tonic immobility reflex.
It is based upon the observation that REM sleep in several mammals (the rat, the hedgehog, the rabbit, and the rhesus monkey) is followed by a brief awakening.
[85][35]: 122–124 [86] Jim Horne, a sleep researcher at Loughborough University, has suggested that REM in modern humans compensates for the reduced need for wakeful food foraging.
