Rapid eye movement sleep
Rapid eye movement sleep (REM sleep or REMS) is a unique phase of
The REM phase is also known as paradoxical sleep (PS) and sometimes desynchronized sleep or dreamy sleep,
REM sleep is physiologically different from the other phases of sleep, which are collectively referred to as
In 1953, Professor
Physiology
Electrical activity in the brain
REM sleep is called "paradoxical" because of its similarities to
During REM sleep, electrical connectivity among different parts of the brain manifests differently than during wakefulness. Frontal and posterior areas are less coherent in most frequencies, a fact which has been cited in relation to the chaotic experience of dreaming. However, the posterior areas are more coherent with each other; as are the right and left hemispheres of the brain, especially during lucid dreams.[13][14]
Brain energy use in REM sleep, as measured by oxygen and glucose metabolism, equals or exceeds energy use in waking. The rate in non-REM sleep is 11–40% lower.[15]
Brain stem
Neural activity during REM sleep seems to originate in the
Forebrain
Research in the 1990s using
The superior frontal gyrus, medial frontal areas, intraparietal sulcus, and superior parietal cortex, areas involved in sophisticated mental activity, show equal activity in REM sleep as in wakefulness. The amygdala is also active during REM sleep and may participate in generating the PGO waves, and experimental suppression of the amygdala results in less REM sleep.[20] The amygdala may also regulate cardiac function in lieu of the less active insular cortex.[7]
Chemicals in the brain
Compared to
Two other
Unlike the abrupt transitions in electrical patterns, the chemical changes in the brain show continuous periodic oscillation.[26]
Models of REM regulation
According to the
Eye movements
Most of the
Circulation, respiration, and thermoregulation
Generally speaking, the body suspends
Erections of the penis (nocturnal penile tumescence or NPT) normally accompany REM sleep in rats and humans.[34]: 169–173 If a male has erectile dysfunction (ED) while awake, but has NPT episodes during REM, it would suggest that the ED is from a psychological rather than a physiological cause. In females, erection of the clitoris (nocturnal clitoral tumescence or NCT) causes enlargement, with accompanying vaginal blood flow and transudation (i.e. lubrication). During a normal night of sleep, the penis and clitoris may be erect for a total time of from one hour to as long as three and a half hours during REM.[35]
Body temperature is not well regulated during REM sleep, and thus organisms become more sensitive to temperatures outside their
Consequently, hot or cold environmental temperatures can reduce the proportion of REM sleep, as well as amount of total sleep.[36][29]: 57–59 In other words, if at the end of a phase of deep sleep, the organism's thermal indicators fall outside of a certain range, it will not enter paradoxical sleep lest deregulation allow temperature to drift further from the desirable value.[29]: 45 This mechanism can be 'fooled' by artificially warming the brain.[29]: 61
Muscle
REM atonia, an almost complete paralysis of the body, is accomplished through the inhibition of
Lack of REM
Lesions of the pons to prevent atonia have induced functional "REM behavior disorder" in animals.[29]: 87
Psychology
Dreaming
Rapid eye movement sleep (REM) has since its discovery been closely associated with dreaming. Waking up sleepers during a REM phase is a common experimental method for obtaining dream reports; 80% of neurotypical people can give some kind of dream report under these circumstances.[41]: 10, 34 [14] 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.[15][42] Lucid dreams are reported far more often in REM sleep.[43] (In fact these could be considered a hybrid state combining essential elements of REM sleep and waking consciousness.)[15] 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.[15] Sometimes, they include elements of the dreamer's recent experience taken directly from episodic memory.[7] By one estimate, 80% of dreams occur during REM.[44]
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.[22][27] However, people woken up during sleep do not report significantly more bizarre dreams during phasic REMS, compared to tonic REMS.[42] 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.[42]
Some dreaming can take place during non-REM sleep. "Light sleepers" can experience dreaming during stage 2 non-REM sleep, whereas "deep sleepers", upon awakening in the same stage, are more likely to report "thinking" but not "dreaming". Certain scientific efforts to assess the uniquely bizarre nature of dreams experienced while asleep were forced to conclude that waking thought could be just as bizarre, especially in conditions of sensory deprivation.[42][45] Because of non-REM dreaming, some sleep researchers have strenuously contested the importance of connecting dreaming to the REM sleep phase. The prospect that well-known neurological aspects of REM do not themselves cause dreaming suggests the need to re-examine the neurobiology of dreaming per se.[41]: 54–57 Some researchers (Dement, Hobson, Jouvet, for example) tend to resist the idea of disconnecting dreaming from REM sleep.[15][34]: 104
Effects of SSRIs
Previous research has shown that
Creativity
After waking from REM sleep, the mind seems "hyperassociative"—more receptive to
Sleep aids the process by which
Timing
In the
During a night of sleep, humans usually experience about four or five periods of REM sleep; they are shorter (~15 min) at the beginning of the night and longer (~25 min) toward the end. 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. The relative amount of REM sleep varies considerably with age. A newborn baby spends more than 80% of total sleep time in REM.[53]
REM sleep typically occupies 20–25% of total sleep in adult humans: about 90–120 minutes of a night's sleep. The first REM episode occurs about 70 minutes after falling asleep. Cycles of about 90 minutes each follow, with each cycle including a larger proportion of REM sleep.[26] (The increased REM sleep later in the night is connected with the circadian rhythm and occurs even in people who did not sleep in the first part of the night.)[54][55]
In the weeks after a human baby is born, as its nervous system matures, neural patterns in sleep begin to show a rhythm of REM and non-REM sleep. (In faster-developing mammals, this process occurs in utero.)[56] Infants spend more time in REM sleep than adults. The proportion of REM sleep then decreases significantly in childhood. Older people tend to sleep less overall, but sleep in REM for about the same absolute time (and therefore spend a greater proportion of sleep in REM).[57][44]
Rapid eye movement sleep can be subclassified into tonic and phasic modes.[58] Tonic REM is characterized by theta rhythms in the brain; phasic REM is characterized by PGO waves and actual "rapid" eye movements. Processing of external stimuli is heavily inhibited during phasic REM, and recent evidence suggests that sleepers are more difficult to arouse from phasic REM than in slow-wave sleep.[17]
Deprivation effects
Selective REMS deprivation causes a significant increase in the number of attempts to go into REM stage while asleep. On recovery nights, an individual will usually move to stage 3 and REM sleep more quickly and experience a REM rebound, which refers to an increase in the time spent in REM stage over normal levels. These findings are consistent with the idea that REM sleep is biologically necessary.[59][60] However, the "rebound" REM sleep usually does not last fully as long as the estimated length of the missed REM periods.[54]
After the deprivation is complete, mild psychological disturbances, such as
It has been suggested that acute REM sleep deprivation can improve certain types of
In other animals
Although it manifests differently in different animals, REM sleep or something like it occurs in all land
The amount of REM sleep and cycling varies among animals; predators experience more REM sleep than prey.
Sleeping reptiles do not seem to have PGO waves or the localized brain activation seen in mammalian REM. However, they do exhibit sleep cycles with phases of REM-like electrical activity measurable by EEG.[68] 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.[69]
Observations of jumping spiders in their nocturnal resting position also suggest a REM sleep-like state characterized by bouts of twitching and retinal movements and hints of muscle atonia (legs curling up as a result of pressure loss caused by muscle atonia in the prosoma).[70]
Sleep deprivation experiments on non-human animals can be set up differently than those on humans. 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.[48]: 686–687 This method also stops working after about 3 days as the subjects (typically rats) lose their will to avoid the water.[55] Another method involves computer monitoring of brain waves, complete with automatic mechanized shaking of the cage when the test animal drifts into REM sleep.[71]
Possible functions
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. In both humans and experimental animals, REM sleep loss leads to several behavioral and physiological abnormalities. Loss of REM sleep has been noticed during various natural and experimental infections. 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.[72] Further, the existence of a "REM rebound" effect suggests the possibility of a biological need for REM sleep.
While the precise function of REM sleep is not well understood, several theories have been proposed.
Memory
Sleep in general aids memory. REM sleep may favor the preservation of certain types of
According to the dual-process hypothesis of sleep and memory, the two major phases of sleep correspond to different types of memory. "Night half" studies have tested this hypothesis with memory tasks either begun before sleep and assessed in the middle of the night, or begun in the middle of the night and assessed in the morning.
Sleep researcher Jerome Siegel has observed that extreme REM deprivation does not significantly interfere with memory. One case study of an individual who had little or no REM sleep due to a shrapnel injury to the brainstem did not find the individual's memory to be impaired. Antidepressants, which suppress REM sleep, show no evidence of impairing memory and may improve it.[65]
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". As a result, those memories which are relevant (whose underlying neuronal substrate is strong enough to withstand such spontaneous, chaotic activation) are further strengthened, whilst weaker, transient, "noise" memory traces disintegrate.[75] Memory consolidation during paradoxical sleep is specifically correlated with the periods of rapid eye movement, which do not occur continuously. One explanation for this correlation is that the PGO electrical waves, which precede the eye movements, also influence memory.[16] 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.[29]: 89
Neural ontogeny
REM sleep prevails most after birth, and diminishes with age. According to the "ontogenetic hypothesis", REM (also known in
Defensive immobilization
Ioannis Tsoukalas of Stockholm University has hypothesized that REM sleep is an evolutionary transformation of a well-known defensive mechanism, the
Shift of gaze
According to "scanning hypothesis", the directional properties of REM sleep are related to a shift of gaze in dream imagery. Against this hypothesis is that such eye movements occur in those born
Oxygen supply to cornea
Dr.
Other theories
Another theory suggests that monoamine shutdown is required so that the monoamine receptors in the brain can recover to regain full sensitivity.
The sentinel hypothesis of REM sleep was put forward by Frederick Snyder in 1966. 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. This does not occur for either cats or humans, although humans are more likely to wake from REM sleep than from NREM sleep. Snyder hypothesized that REM sleep activates an animal periodically, to scan the environment for possible predators. This hypothesis does not explain the muscle paralysis of REM sleep; however, a logical analysis might suggest that the
Jim Horne, a sleep researcher at Loughborough University, has suggested that REM in modern humans compensates for the reduced need for wakeful food foraging.[10]
Other theories are that REM sleep warms the brain, stimulates and stabilizes the
Furthermore, eye movements are also theorized to play a role in certain psychotherapies such as eye movement desensitization and reprocessing (EMDR).
See also
References
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Further reading
- Antrobus JS, Bertini M (1992). The Neuropsychology of Sleep and Dreaming. Hillsdale, NJ: Lawrence Erlbaum Associates. ISBN 0-8058-0925-2.
- Ellman SJ, Antrobus JS (1991). The Mind in Sleep: Psychology and Psychophysiology (Second ed.). John Wiley & Sons, Inc. ISBN 0-471-52556-1.
- Mallick BA, Pandi-Perumal SR, McCarley RW, Morrison AR (2011). Rapid Eye Movement Sleep: Regulation and Function. Cambridge University Press. ISBN 978-0-521-11680-0.
- Monti JM, Pandi-Perumal SR, Sinton CM (2008). Neurochemistry of Sleep and Wakefulness. Cambridge University Press. ISBN 978-0-521-86441-1.
- Lee CW, Cuijpers P (June 2013). "A meta-analysis of the contribution of eye movements in processing emotional memories". Journal of Behavior Therapy and Experimental Psychiatry. 44 (2): 231–9. PMID 23266601.
- Snyder F (August 1966). "Toward an evolutionary theory of dreaming". The American Journal of Psychiatry. 123 (2): 121–142. PMID 5329927.
- Edward F. Pace-Schott, ed. (2003). Sleep and Dreaming: Scientific Advances and Reconsiderations. Cambridge University Press. ISBN 978-0-521-00869-3.
- Koulack D (1991). To Catch A Dream: Explorations of Dreaming. New York: SUNY.
- Nguyen TQ, Liang CL, Marks GA (August 2013). "GABA(A) receptors implicated in REM sleep control express a benzodiazepine binding site". Brain Research. 1527: 131–140. PMID 23835499.
- Liang CL, Marks GA (January 2014). "GABAA receptors are located in cholinergic terminals in the nucleus pontis oralis of the rat: implications for REM sleep control". Brain Research. 1543: 58–64. S2CID 46317814.
- Grace KP, Vanstone LE, Horner RL (October 2014). "Endogenous cholinergic input to the pontine REM sleep generator is not required for REM sleep to occur". The Journal of Neuroscience. 34 (43): 14198–14209. PMID 25339734.
- Moreland RB, Nehra A (1999). "Pathosphysiology of erectile dysfunction; a molecular basis, role of NPT in maintaining potency". In Carson III CC, Kirby RS, Goldstein I (eds.). Textbook of Erectile Dysfunction. Oxford, U.K.: Isis Medical Media, Ltd. pp. 105–115.
External links
- PBS' NOVA episode "What Are Dreams?" Video and Transcript
- LSDBase – an open sleep research database with images of REM sleep recordings.