Rapid eye movement
Encyclopedia
Rapid eye movement sleep (REM sleep) is a normal stage of sleep
characterized by the random movement of the eyes. REM sleep is classified into two categories: tonic and phasic. It was identified and defined by Nathaniel Kleitman
, Eugene Aserinsky
, and Jon Birtwell in the early 1950s. Criteria for REM sleep includes rapid eye movement, but also low muscle tone and a rapid, low-voltage EEG
; these features are easily discernible in a polysomnogram , the sleep study typically done for patients with suspected sleep disorders.
REM sleep in adult humans typically occupies 20–25% of total sleep, about 90–120 minutes of a night's sleep. During a normal night of sleep, humans usually experience about four or five periods of REM sleep; they are quite short at the beginning of the night and longer 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. During REM, the activity of the brain's neuron
s is quite similar to that during waking hours; for this reason, the REM-sleep stage may be called paradoxical sleep.
REM sleep is physiologically different from the other phases of sleep, which are collectively referred to as non-REM sleep (NREM sleep). Subjects vividly recalled dream
s mostly occur during REM sleep.
Physiologically, certain neurons in the brain stem
, known as REM sleep-on cells, (located in the pontine tegmentum
), are particularly active during REM sleep, and are probably responsible for its occurrence. The release of certain neurotransmitter
s, the monoamines (norepinephrine
, serotonin
and histamine
), is completely shut down during REM. This causes REM atonia, a state in which the motor neuron
s are not stimulated and thus the body's muscles do not move. Lack of such REM atonia causes REM behavior disorder; sufferers act out the movements occurring in their dreams.
Heart rate
and breathing rate
are irregular during REM sleep, again similar to the waking hours. Body temperature is not well regulated during REM. Erection
s of the penis
(nocturnal penile tumescence
or NPT) normally accompany REM sleep. 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. Research urologists have found that the increased blood flow during NPT and NCT episodes may prevent excessive collagen from forming in the erectile tissues (sinusoids) of the clitoris and penis.
In a study published in the journal Human Brain Mapping, participants who were in REM "dream" sleep were also monitored by special MRI imaging designed to visualize brain activity. The researchers found activity in areas of the brain that control sight, hearing, smell, touch, arousal, sleep-wake transitions, balance and body movement.
The eye movements associated with REM are generated by the pontine
nucleus with projections to the superior colliculus
and are associated with PGO waves
(Ponto-geniculo-occipital waves).
During dreaming, the primary visual cortex
is inactive, while secondary areas are active. This is similar to when subjects are asked to imagine or recall a visual scene, and different from what happens when they are actually seeing the scene.
and spatial memory
. (Slow-wave sleep
, part of non-REM sleep, appears to be important for declarative memory
.) A recent study shows that artificial enhancement of the non-REM sleep improves the next-day recall of memorized pairs of words. Tucker et al. demonstrated that a daytime nap containing solely non-REM sleep enhances declarative memory
but not procedural memory
. The role of REM sleep in memory, however, is not without its doubts. Monoamine oxidase (MAO) inhibitors
and tricyclic antidepressants can suppress REM sleep, yet these drugs show no evidence of impairing memory. On the contrary, some studies show MAO inhibitors improve memory. Moreover, 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. (For a more detailed critique on the link between sleep and memory, see Ref.)
Intimately related to views on REM function in memory consolidation, Mitchison and Crick
have proposed 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", which 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.
One important theoretical consequence of the Ontogenetic Hypothesis is that REM sleep may have no essentially vital function in the mature brain, i.e., once the development of CNS has completed. However, because processes of neuronal plasticity do not cease altogether in the brain, REM sleep may continue to be implicated in neurogenesis in adults as a source of sustained spontaneous stimulation.
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. Although, sleep deprivation in general annoys most of the general population, it has recurrently been shown to alleviate depression, albeit temporarily. More than half the individuals who experience this relief report it to be rendered ineffective after sleeping the following night. Thus, researchers have devised methods such as altering the sleep schedule for a span of days following a REM deprivation period and combining sleep-schedule alterations with pharmacotherapy to prolong this effect. Though most antidepressant
s selectively inhibit REM sleep due to their action on monoamines, this effect decreases after long-term use. It is interesting to note that REM sleep deprivation stimulates hippocampal neurogenesis much the same as antidepressants and also psilocybin
.
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.
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. Although a logical analysis might suggest that the muscle paralysis exists to prevent the "awakening" animal for waking up unnecessarily and allowing it to return easily to deeper sleep.
forms associative elements into new combinations that are useful or meet some requirement. This occurs in REM sleep rather than in NREM sleep. Rather than being due to memory processes, this has been attributed to changes during REM sleep in cholinergic
and noradrenergic neuromodulation. During REM sleep high levels of acetylcholine in the hippocampus
suppress feedback from hippocampus to the neocortex
, and lower levels of acetylcholine and norepinephrine in the neocortex encourage the spread of associational activity within neocortical areas without control from the hippocampus. This is in contrast to waking consciousness, where higher levels of norepinephrine and acetylcholine inhibit recurrent connections in the neocortex. 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."
and in fetuses in spite of lack of vision. Also binocular
REMs are non-conjugated and so lack a fixation point. In support, research finds that in goal-oriented dreams, eye gaze is directed towards the action described by the dreamer.
Other theories are that they lubricate the cornea
, warm the brain, stimulate and stabilize the neural circuits that have not been activated during waking
, create internal stimulation to aid development of the CNS
, or lack any purpose, being random creation of brain activation.
and Nathaniel Kleitman
with assistance from William C. Dement
, a medical student at the time, in 1952 during their tenures at the University of Chicago
. Kleitmann and Aserinsky's seminal article was published September 10, 1953.
Sleep
Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than...
characterized by the random movement of the eyes. REM sleep is classified into two categories: tonic and phasic. It was identified and defined by Nathaniel Kleitman
Nathaniel Kleitman
Nathaniel Kleitman was Professor Emeritus in Physiology at the University of Chicago. Author of the seminal 1939 book Sleep and Wakefulness, he is recognized as the father of American sleep research...
, Eugene Aserinsky
Eugene Aserinsky
Eugene Aserinsky , a pioneer in sleep research, was a graduate student at University of Chicago in 1953 when he discovered REM sleep. He made the discovery after hours spent studying the eyelids of sleeping subjects...
, and Jon Birtwell in the early 1950s. Criteria for REM sleep includes rapid eye movement, but also low muscle tone and a rapid, low-voltage EEG
EEG
EEG commonly refers to electroencephalography, a measurement of the electrical activity of the brain.EEG may also refer to:* Emperor Entertainment Group, a Hong Kong-based entertainment company...
; these features are easily discernible in a polysomnogram , the sleep study typically done for patients with suspected sleep disorders.
REM sleep in adult humans typically occupies 20–25% of total sleep, about 90–120 minutes of a night's sleep. During a normal night of sleep, humans usually experience about four or five periods of REM sleep; they are quite short at the beginning of the night and longer 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. During REM, the activity of the brain's neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s is quite similar to that during waking hours; for this reason, the REM-sleep stage may be called paradoxical sleep.
REM sleep is physiologically different from the other phases of sleep, which are collectively referred to as non-REM sleep (NREM sleep). Subjects vividly recalled dream
Dream
Dreams are successions of images, ideas, emotions, and sensations that occur involuntarily in the mind during certain stages of sleep. The content and purpose of dreams are not definitively understood, though they have been a topic of scientific speculation, philosophical intrigue and religious...
s mostly occur during REM sleep.
Physiology
Brain stem
In vertebrate anatomy the brainstem is the posterior part of the brain, adjoining and structurally continuous with the spinal cord. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves...
, known as REM sleep-on cells, (located in the pontine tegmentum
Pontine tegmentum
The pontine tegmentum is a part of the pons of the brain involved in the initiation of REM sleep. It includes the pedunculopontine nucleus and the laterodorsal tegmental nucleus, among others, and is located near the raphe nucleus and the locus ceruleus....
), are particularly active during REM sleep, and are probably responsible for its occurrence. The release of certain neurotransmitter
Neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...
s, the monoamines (norepinephrine
Norepinephrine
Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...
, serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
and histamine
Histamine
Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by...
), is completely shut down during REM. This causes REM atonia, a state in which the motor neuron
Motor neuron
In vertebrates, the term motor neuron classically applies to neurons located in the central nervous system that project their axons outside the CNS and directly or indirectly control muscles...
s are not stimulated and thus the body's muscles do not move. Lack of such REM atonia causes REM behavior disorder; sufferers act out the movements occurring in their dreams.
Heart rate
Heart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....
and breathing rate
Respiratory rate
Respiratory rate is also known by respiration rate, pulmonary ventilation rate, ventilation rate, or breathing frequency is the number of breaths taken within a set amount of time, typically 60 seconds....
are irregular during REM sleep, again similar to the waking hours. Body temperature is not well regulated during REM. Erection
Erection
Penile erection is a physiological phenomenon where the penis becomes enlarged and firm. Penile erection is the result of a complex interaction of psychological, neural, vascular and endocrine factors, and is usually, though not exclusively, associated with sexual arousal...
s of the penis
Penis
The penis is a biological feature of male animals including both vertebrates and invertebrates...
(nocturnal penile tumescence
Nocturnal penile tumescence
Nocturnal penile tumescence is the spontaneous occurrence of an erection of the penis during sleep. All men without physiological erectile dysfunction experience this phenomenon, usually three to five times during the night...
or NPT) normally accompany REM sleep. 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
Clitoris
The clitoris is a sexual organ that is present only in female mammals. In humans, the visible button-like portion is located near the anterior junction of the labia minora, above the opening of the urethra and vagina. Unlike the penis, which is homologous to the clitoris, the clitoris does not...
(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. Research urologists have found that the increased blood flow during NPT and NCT episodes may prevent excessive collagen from forming in the erectile tissues (sinusoids) of the clitoris and penis.
In a study published in the journal Human Brain Mapping, participants who were in REM "dream" sleep were also monitored by special MRI imaging designed to visualize brain activity. The researchers found activity in areas of the brain that control sight, hearing, smell, touch, arousal, sleep-wake transitions, balance and body movement.
The eye movements associated with REM are generated by the pontine
Pons
The pons is a structure located on the brain stem, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio . It is superior to the medulla oblongata, inferior to the midbrain, and ventral to the cerebellum. In humans and other bipeds this means it...
nucleus with projections to the superior colliculus
Superior colliculus
The optic tectum or simply tectum is a paired structure that forms a major component of the vertebrate midbrain. In mammals this structure is more commonly called the superior colliculus , but, even in mammals, the adjective tectal is commonly used. The tectum is a layered structure, with a...
and are associated with PGO waves
PGO waves
Ponto-geniculo-occipital waves or PGO waves are phasic field potentials. These waves can be recorded from the pons, the lateral geniculate nucleus , and the occipital cortex regions of the brain, where these waveforms originate...
(Ponto-geniculo-occipital waves).
During dreaming, the primary visual cortex
Visual cortex
The visual cortex of the brain is the part of the cerebral cortex responsible for processing visual information. It is located in the occipital lobe, in the back of the brain....
is inactive, while secondary areas are active. This is similar to when subjects are asked to imagine or recall a visual scene, and different from what happens when they are actually seeing the scene.
Theories about the function(s) of REM sleep
The function of REM sleep is not well understood; several theories have been proposed.Memory-related theories
According to one theory, certain memories are consolidated during REM sleep. Numerous studies have suggested that REM sleep is important for consolidation of procedural memoryProcedural memory
Procedural memory is memory for how to do things. Procedural memory guides the processes we perform and most frequently resides below the level of conscious awareness. When needed, procedural memories are automatically retrieved and utilized for the execution of the integrated procedures involved...
and spatial memory
Spatial memory
In cognitive psychology and neuroscience, spatial memory is the part of memory responsible for recording information about one's environment and its spatial orientation. For example, a person's spatial memory is required in order to navigate around a familiar city, just as a rat's spatial memory is...
. (Slow-wave sleep
Slow-wave sleep
Slow-wave sleep , often referred to as deep sleep, consists of stages 3 and 4 of non-rapid eye movement sleep, according to the Rechtschaffen & Kales standard of 1968. As of 2008, the American Academy of Sleep Medicine has discontinued the use of stage 4, such that the previous stages 3 and 4 now...
, part of non-REM sleep, appears to be important for declarative memory
Declarative memory
Declarative memory is one of two types of long term human memory. It refers to memories which can be consciously recalled such as facts and knowledge. Its counterpart is known as non-declarative or Procedural memory, which refers to unconscious memories such as skills...
.) A recent study shows that artificial enhancement of the non-REM sleep improves the next-day recall of memorized pairs of words. Tucker et al. demonstrated that a daytime nap containing solely non-REM sleep enhances declarative memory
Declarative memory
Declarative memory is one of two types of long term human memory. It refers to memories which can be consciously recalled such as facts and knowledge. Its counterpart is known as non-declarative or Procedural memory, which refers to unconscious memories such as skills...
but not procedural memory
Procedural memory
Procedural memory is memory for how to do things. Procedural memory guides the processes we perform and most frequently resides below the level of conscious awareness. When needed, procedural memories are automatically retrieved and utilized for the execution of the integrated procedures involved...
. The role of REM sleep in memory, however, is not without its doubts. Monoamine oxidase (MAO) inhibitors
Monoamine oxidase inhibitor
Monoamine oxidase inhibitors are a class of antidepressant drugs prescribed for the treatment of depression. They are particularly effective in treating atypical depression....
and tricyclic antidepressants can suppress REM sleep, yet these drugs show no evidence of impairing memory. On the contrary, some studies show MAO inhibitors improve memory. Moreover, 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. (For a more detailed critique on the link between sleep and memory, see Ref.)
Intimately related to views on REM function in memory consolidation, Mitchison and Crick
Francis Crick
Francis Harry Compton Crick OM FRS was an English molecular biologist, biophysicist, and neuroscientist, and most noted for being one of two co-discoverers of the structure of the DNA molecule in 1953, together with James D. Watson...
have proposed 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", which process they characterize as "unlearning
Reverse learning
Reverse learning is a neurobiological theory of dreams. In 1983, in a paper published in the famous science journal Nature, Crick and Mitchison's reverse learning model likened the process of dreaming to a computer in that it was "off-line" during dreaming or the REM phase of sleep...
". 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.
Stimulation in CNS development as a primary function
According to another theory, known as the Ontogenetic Hypothesis of REM sleep, this sleep stage (also known as active sleep in neonates) is particularly important to the developing brain, possibly because it provides the neural stimulation that newborns need to form mature neural connections and for proper nervous system development. Studies investigating the effects of active sleep deprivation have shown that deprivation early in life can result in behavioral problems, permanent sleep disruption, decreased brain mass, and result in an abnormal amount of neuronal cell death. Further supporting this theory is the fact that the amount of REM sleep in humans decreases with age, as well as data from other species (see below).One important theoretical consequence of the Ontogenetic Hypothesis is that REM sleep may have no essentially vital function in the mature brain, i.e., once the development of CNS has completed. However, because processes of neuronal plasticity do not cease altogether in the brain, REM sleep may continue to be implicated in neurogenesis in adults as a source of sustained spontaneous stimulation.
Other theories
Yet another theory suggests that monoamine shutdown is required so that the monoamine receptors in the brain can recover to regain full sensitivity. Indeed, if REM sleep is repeatedly interrupted, the person will compensate for it with longer REM sleep, "rebound sleep", at the next opportunity. The only way to cure it is to sleep early.It has been suggested that acute REM sleep deprivation can improve certain types of depression
Clinical depression
Major depressive disorder is a mental disorder characterized by an all-encompassing low mood accompanied by low self-esteem, and by loss of interest or pleasure in normally enjoyable activities...
when depression appears to be related to an imbalance of certain neurotransmitters. Although, sleep deprivation in general annoys most of the general population, it has recurrently been shown to alleviate depression, albeit temporarily. More than half the individuals who experience this relief report it to be rendered ineffective after sleeping the following night. Thus, researchers have devised methods such as altering the sleep schedule for a span of days following a REM deprivation period and combining sleep-schedule alterations with pharmacotherapy to prolong this effect. Though most antidepressant
Antidepressant
An antidepressant is a psychiatric medication used to alleviate mood disorders, such as major depression and dysthymia and anxiety disorders such as social anxiety disorder. According to Gelder, Mayou &*Geddes people with a depressive illness will experience a therapeutic effect to their mood;...
s selectively inhibit REM sleep due to their action on monoamines, this effect decreases after long-term use. It is interesting to note that REM sleep deprivation stimulates hippocampal neurogenesis much the same as antidepressants and also psilocybin
Psilocybin
Psilocybin is a naturally occurring psychedelic prodrug, with mind-altering effects similar to those of LSD and mescaline, after it is converted to psilocin. The effects can include altered thinking processes, perceptual distortions, an altered sense of time, and spiritual experiences, as well as...
.
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.
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. Although a logical analysis might suggest that the muscle paralysis exists to prevent the "awakening" animal for waking up unnecessarily and allowing it to return easily to deeper sleep.
Effect of sleep deprivation on REM sleep
Studies have shown that people sleep more efficiently when they are sleep-deprived and that they enter REM sleep faster when this is the case. Sleep studies also show that patients who sleep less move to stage 3 and REM sleep faster than patients who are not sleep deprived.REM sleep and creativity
Sleep aids the process by which creativityCreativity
Creativity refers to the phenomenon whereby a person creates something new that has some kind of value. What counts as "new" may be in reference to the individual creator, or to the society or domain within which the novelty occurs...
forms associative elements into new combinations that are useful or meet some requirement. This occurs in REM sleep rather than in NREM sleep. Rather than being due to memory processes, this has been attributed to changes during REM sleep in cholinergic
Cholinergic
The word choline generally refers to the various quaternary ammonium salts containing the N,N,N-trimethylethanolammonium cation. Found in most animal tissues, choline is a primary component of the neurotransmitter acetylcholine and functions with inositol as a basic constituent of lecithin...
and noradrenergic neuromodulation. During REM sleep high levels of acetylcholine in the hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
suppress feedback from hippocampus to the neocortex
Neocortex
The neocortex , also called the neopallium and isocortex , is a part of the brain of mammals. It is the outer layer of the cerebral hemispheres, and made up of six layers, labelled I to VI...
, and lower levels of acetylcholine and norepinephrine in the neocortex encourage the spread of associational activity within neocortical areas without control from the hippocampus. This is in contrast to waking consciousness, where higher levels of norepinephrine and acetylcholine inhibit recurrent connections in the neocortex. 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."
Theories about the function of rapid eye movements
According to "scanning hypothesis" the directional properties of REM sleep eye movements are related to shifts of gaze in dream imagery. Against this hypothesis is that such eye movements occur in those born blindBlindness
Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...
and in fetuses in spite of lack of vision. Also binocular
Binocular vision
Binocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a...
REMs are non-conjugated and so lack a fixation point. In support, research finds that in goal-oriented dreams, eye gaze is directed towards the action described by the dreamer.
Other theories are that they lubricate the cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
, warm the brain, stimulate and stabilize the neural circuits that have not been activated during waking
Waking Up
Waking Up is a solo album by Topper Headon best known as the drummer of The Clash. The album was released by Mercury in 1986 with a cover photograph taken by Tim White. "Leave It to Luck" was released as a single and as part of an EP...
, create internal stimulation to aid development of the CNS
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
, or lack any purpose, being random creation of brain activation.
Discovery
The phenomenon of REM sleep and its association with dreaming was discovered by Eugene AserinskyEugene Aserinsky
Eugene Aserinsky , a pioneer in sleep research, was a graduate student at University of Chicago in 1953 when he discovered REM sleep. He made the discovery after hours spent studying the eyelids of sleeping subjects...
and Nathaniel Kleitman
Nathaniel Kleitman
Nathaniel Kleitman was Professor Emeritus in Physiology at the University of Chicago. Author of the seminal 1939 book Sleep and Wakefulness, he is recognized as the father of American sleep research...
with assistance from William C. Dement
William C. Dement
William Charles Dement is a pioneering US sleep researcher, and founder of the Sleep Research Center, the world's first sleep laboratory, at Stanford University. He is a leading authority on sleep, sleep deprivation, and the diagnosis and treatment of sleep disorders such as sleep apnea and...
, a medical student at the time, in 1952 during their tenures at the University of Chicago
University of Chicago
The University of Chicago is a private research university in Chicago, Illinois, USA. It was founded by the American Baptist Education Society with a donation from oil magnate and philanthropist John D. Rockefeller and incorporated in 1890...
. Kleitmann and Aserinsky's seminal article was published September 10, 1953.
See also
- Sleep and learningSleep and learningMany competing theories have been advanced to discover the possible connections between sleep and learning in humans. One theory is that sleep consolidates and optimizes the layout of memories, though recent evidence suggests this may be restricted to implicit procedural memories.-Increased...
- DreamDreamDreams are successions of images, ideas, emotions, and sensations that occur involuntarily in the mind during certain stages of sleep. The content and purpose of dreams are not definitively understood, though they have been a topic of scientific speculation, philosophical intrigue and religious...
- NREMNREMNon-rapid eye movement, or NREM is, collectively, sleep stages 1 – 3, previously known as stages 1 – 4. Rapid eye movement sleep is not included. There are distinct electroencephalographic and other characteristics seen in each stage. Unlike REM sleep, there is usually little or no eye movement...
- Lucid Dream
- Pedunculopontine nucleusPedunculopontine nucleusThe pedunculopontine nucleus is located in the brainstem, caudal to the substantia nigra and adjacent to the superior cerebellar peduncle. It has two divisions, one containing cholinergic neurons, the pars compacta, and one containing mostly glutamatergic neurons, the pars dissipata...
(PPN) - PGO wavesPGO wavesPonto-geniculo-occipital waves or PGO waves are phasic field potentials. These waves can be recorded from the pons, the lateral geniculate nucleus , and the occipital cortex regions of the brain, where these waveforms originate...
- REM ReboundREM reboundREM rebound is the lengthening and increasing frequency and depth of REM sleep which occurs after periods of sleep deprivation. When people are prevented from experiencing REM, they take less time than usual to attain the REM state....