Slow-wave sleep
Encyclopedia
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 (R & K) standard of 1968. As of 2008, the American Academy of Sleep Medicine
(AASM) has discontinued the use of stage 4, such that the previous stages 3 and 4 now are combined as stage 3. An epoch (30 seconds of sleep) which consists of 20% or more slow wave (delta) sleep, now is considered to be stage 3.
The highest arousal thresholds (i.e. difficulty of awakening, such as by a sound of a particular volume) are observed in deep sleep. A person will typically feel more groggy when awoken from slow-wave sleep, and indeed, cognitive tests administered after awakening then indicate that mental performance is somewhat impaired for periods of up to 30 minutes or so, relative to awakenings from other stages. This phenomenon has been called "sleep inertia
."
After sleep deprivation
there is a sharp rebound of SWS, suggesting its homeostatic control.
The major factor determining how much slow-wave sleep is observed in a given sleep period is the duration of preceding wakefulness, likely related to accumulation of sleep-promoting substances in the brain. Some of the few factors known to increase slow-wave sleep in the sleep period that follows them include body heating (as by immersion in a hot tub), high carbohydrate ingestion, and intense prolonged exercise. The latter probably exerts its influence by increasing body temperature.
In addition to these factors, the duration of SWS periods can be increased by ingestion of THC
, SSRIs, and other drugs. In instances such as these, TST (Total Sleep Time) is often unaffected due to circadian rhythms and/or a person's alarm clock and early morning obligations. This increase of SWS can lead to increased REM latency and a decrease in REM period durations. If the total time spent in REM is decreased long enough and repeatedly over a substantial number of nights a "REM rebound" will occur in response to removal of its inhibitor. An increase in REM is believed to produce symptoms of depression and bipolar disorder in many patients for an amount of time relative to the severity of the previous "REM suppression." It is debatable whether or not this could explain the return in symptoms of depression disorder after removal of SSRI medications.
Certain substances, such as benzodiazepines (e.g. Ativan, Valium, Klonopin) seem to have the reverse effect on the time spent in SWS. Instead of lengthening SWS (as do the substances mentioned above), they are known to shorten the time. While these sedatives can increase sleep duration or shorten the time it takes before sleep-onset occurs, they tend to deprive patients of deep sleep.
The chemical gamma-Hydroxybutyric acid
(GHB) is known to promote SWS. In the United States, the Food and Drug Administration
permits the use of GHB under the trade name Xyrem
to reduce cataplexy
attacks and excessive daytime sleepiness in patients with narcolepsy
.
In an online press release, dated Tuesday, August 30, 2011, from Harvard University Medical School-affiliate Brigham and Women's Hospital
's Division of Sleep Medicine:
"New research from Brigham and Women's Hospital (BWH) conducted in collaboration with California Pacific Medical Center
and six clinical sites across the U.S. finds that reduced slow wave sleep(SWS) is a powerful predictor for developing high blood pressure in older men. This research is published in "Hypertension: Journal of the American Heart Association.""
Large 75-microvolt (0.5–2 Hz) delta wave
s predominate the electroencephalogram (EEG). Stage N3 is defined by the presence of 20% delta wave
s in any given 30-second epoch of the EEG during sleep, by the current 2007 AASM guidelines.
Longer periods of slow-wave sleep occur in the first part of the night, primarily in the first two sleep cycles (roughly 3 hours). Children and young adults will have more total slow-wave sleep in a night than older adults. The elderly may not go into slow-wave sleep at all during many nights of sleep.
Slow-wave sleep (SWS) is an active phenomenon probably brought about by the activation of serotonergic
neurons of the raphe
system.
The slow wave seen in the cortical EEG is generated through thalamocortical communication through the thalamocortical neuron
s. In the TC neurons this is generated by the "slow oscillation" and is dependent on membrane potential
bistability
, a property of these neurons due to an electrophysiological component known as I t Window. I t Window is due to the overlap underneath activation/inactivation curves if plotted for T-type calcium channels (inward current). If these two curves are multiplied, and another line superimposed on the graph to show a small Ik leak current (outward), then the interplay between these inward (I t Window) and outward (small Ik leak), three equilibrium points are seen at −90, −70 and −60 mv, −90 and −60 being stable and −70 unstable. This property allows the generation of slow waves due to an oscillation between two stable points. It is important to note that in in vitro
, mGluR must be activated on these neurons to allow a small Ik leak, as seen in in vivo
situations.
American Academy of Sleep Medicine
The American Academy of Sleep Medicine is a United States professional society for the medical subspecialty of sleep medicine. It was established in 1975. The AASM is the only professional society that is dedicated exclusively to the medical subspecialty of sleep medicine...
(AASM) has discontinued the use of stage 4, such that the previous stages 3 and 4 now are combined as stage 3. An epoch (30 seconds of sleep) which consists of 20% or more slow wave (delta) sleep, now is considered to be stage 3.
The highest arousal thresholds (i.e. difficulty of awakening, such as by a sound of a particular volume) are observed in deep sleep. A person will typically feel more groggy when awoken from slow-wave sleep, and indeed, cognitive tests administered after awakening then indicate that mental performance is somewhat impaired for periods of up to 30 minutes or so, relative to awakenings from other stages. This phenomenon has been called "sleep inertia
Sleep inertia
Sleep inertia is a physiological state characterised by a decline in motor dexterity and a subjective feeling of grogginess immediately following an abrupt awakening. The impaired alertness may interfere with the ability to perform mental or physical tasks...
."
After sleep deprivation
Sleep deprivation
Sleep deprivation is the condition of not having enough sleep; it can be either chronic or acute. A chronic sleep-restricted state can cause fatigue, daytime sleepiness, clumsiness and weight loss or weight gain. It adversely affects the brain and cognitive function. Few studies have compared the...
there is a sharp rebound of SWS, suggesting its homeostatic control.
The major factor determining how much slow-wave sleep is observed in a given sleep period is the duration of preceding wakefulness, likely related to accumulation of sleep-promoting substances in the brain. Some of the few factors known to increase slow-wave sleep in the sleep period that follows them include body heating (as by immersion in a hot tub), high carbohydrate ingestion, and intense prolonged exercise. The latter probably exerts its influence by increasing body temperature.
In addition to these factors, the duration of SWS periods can be increased by ingestion of THC
THC
THC commonly refers to tetrahydrocannabinol, the main active chemical compound in Cannabis.THC may also refer to:* Tan Holdings Corporation...
, SSRIs, and other drugs. In instances such as these, TST (Total Sleep Time) is often unaffected due to circadian rhythms and/or a person's alarm clock and early morning obligations. This increase of SWS can lead to increased REM latency and a decrease in REM period durations. If the total time spent in REM is decreased long enough and repeatedly over a substantial number of nights a "REM rebound" will occur in response to removal of its inhibitor. An increase in REM is believed to produce symptoms of depression and bipolar disorder in many patients for an amount of time relative to the severity of the previous "REM suppression." It is debatable whether or not this could explain the return in symptoms of depression disorder after removal of SSRI medications.
Certain substances, such as benzodiazepines (e.g. Ativan, Valium, Klonopin) seem to have the reverse effect on the time spent in SWS. Instead of lengthening SWS (as do the substances mentioned above), they are known to shorten the time. While these sedatives can increase sleep duration or shorten the time it takes before sleep-onset occurs, they tend to deprive patients of deep sleep.
The chemical gamma-Hydroxybutyric acid
Gamma-Hydroxybutyric acid
γ-Hydroxybutyric acid , also known as 4-hydroxybutanoic acid and sodium oxybate when used for medicinal purposes, is a naturally occurring substance found in the central nervous system, wine, beef, small citrus fruits, and almost all animals in small amounts. It is also categorized as an illegal...
(GHB) is known to promote SWS. In the United States, the Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
permits the use of GHB under the trade name Xyrem
Xyrem
Xyrem is a prescription medication manufactured by Jazz Pharmaceuticals, and is approved by the U.S. Food and Drug Administration for the treatment of cataplexy associated with narcolepsy and Excessive Daytime Sleepiness associated with narcolepsy...
to reduce cataplexy
Cataplexy
Cataplexy is a sudden and transient episode of loss of muscle tone, often triggered by emotions. It is a rare disease , but affects roughly 70% of people who have narcolepsy...
attacks and excessive daytime sleepiness in patients with narcolepsy
Narcolepsy
Narcolepsy is a chronic sleep disorder, or dyssomnia, characterized by excessive sleepiness and sleep attacks at inappropriate times, such as while at work. People with narcolepsy often experience disturbed nocturnal sleep and an abnormal daytime sleep pattern, which often is confused with insomnia...
.
In an online press release, dated Tuesday, August 30, 2011, from Harvard University Medical School-affiliate Brigham and Women's Hospital
Brigham and Women's Hospital
Brigham and Women's Hospital is the largest hospital of the Longwood Medical and Academic Area in Boston, Massachusetts. It is directly adjacent to Harvard Medical School of which it is the second largest teaching affiliate with 793 beds...
's Division of Sleep Medicine:
"New research from Brigham and Women's Hospital (BWH) conducted in collaboration with California Pacific Medical Center
California Pacific Medical Center
California Pacific Medical Center is one of the largest private, non-profit, academic medical centers in Northern California. The Medical Center is a combination of four of San Francisco's oldest medical institutions: Pacific Presbyterian Hospital, Children's Hospital of San Francisco, Davies...
and six clinical sites across the U.S. finds that reduced slow wave sleep(SWS) is a powerful predictor for developing high blood pressure in older men. This research is published in "Hypertension: Journal of the American Heart Association.""
Electroencephalographic characteristics
Delta wave
A delta wave is a high amplitude brain wave with a frequency of oscillation between 0–4 hertz. Delta waves, like other brain waves, are recorded with an electroencephalogram and are usually associated with the deepest stages of sleep , also known as slow-wave sleep , and aid in characterizing the...
s predominate the electroencephalogram (EEG). Stage N3 is defined by the presence of 20% delta wave
Delta wave
A delta wave is a high amplitude brain wave with a frequency of oscillation between 0–4 hertz. Delta waves, like other brain waves, are recorded with an electroencephalogram and are usually associated with the deepest stages of sleep , also known as slow-wave sleep , and aid in characterizing the...
s in any given 30-second epoch of the EEG during sleep, by the current 2007 AASM guidelines.
Longer periods of slow-wave sleep occur in the first part of the night, primarily in the first two sleep cycles (roughly 3 hours). Children and young adults will have more total slow-wave sleep in a night than older adults. The elderly may not go into slow-wave sleep at all during many nights of sleep.
Slow-wave sleep (SWS) is an active phenomenon probably brought about by the activation of serotonergic
Serotonergic
Serotonergic or serotoninergic means "related to the neurotransmitter serotonin". A synapse is serotonergic if it uses serotonin as its neurotransmitter...
neurons of the raphe
Raphe
Raphe has several different meanings in science. Pronounced .In botany and planktology it is commonly used when describing a seam or ridge on diatoms or seeds....
system.
The slow wave seen in the cortical EEG is generated through thalamocortical communication through the thalamocortical 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. In the TC neurons this is generated by the "slow oscillation" and is dependent on membrane potential
Membrane potential
Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...
bistability
Bistability
Bistability is a fundamental phenomenon in nature. Something that is bistable can be resting in either of two states. These rest states need not be symmetric with respect to stored energy...
, a property of these neurons due to an electrophysiological component known as I t Window. I t Window is due to the overlap underneath activation/inactivation curves if plotted for T-type calcium channels (inward current). If these two curves are multiplied, and another line superimposed on the graph to show a small Ik leak current (outward), then the interplay between these inward (I t Window) and outward (small Ik leak), three equilibrium points are seen at −90, −70 and −60 mv, −90 and −60 being stable and −70 unstable. This property allows the generation of slow waves due to an oscillation between two stable points. It is important to note that in in vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
, mGluR must be activated on these neurons to allow a small Ik leak, as seen in in vivo
In vivo
In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...
situations.
See also
- Non-rapid eye movement sleep (NREM)
- Unihemispheric slow-wave sleepUnihemispheric slow-wave sleepUnihemispheric slow-wave sleep , also termed asymmetric slow-wave sleep , is characterized by slow-wave activity in one hemisphere of the brain while a low voltage EEG, characteristic of wakefulness, is present in the other. The phenomenon has been observed in a number of terrestrial and aquatic as...
- Delta sleep-inducing peptideDelta sleep-inducing peptideDelta sleep-inducing peptide, abbreviated DSIP, is a neuropeptide that when infused into the mesodiencephalic ventricle ofrecipient rabbits induces spindle and delta EEG activity and reduced motor activities....
- 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...
- PreconsciousPreconsciousIn Freudian psychoanalysis, the word preconscious is applied to thoughts which are unconscious at the particular moment in question, but which are not repressed and are therefore available for recall and easily capable of becoming conscious....
- Unconscious mindUnconscious mindThe unconscious mind is a term coined by the 18th century German romantic philosopher Friedrich Schelling and later introduced into English by the poet and essayist Samuel Taylor Coleridge...
- SubconsciousSubconsciousThe term subconscious is used in many different contexts and has no single or precise definition. This greatly limits its significance as a definition-bearing concept, and in consequence the word tends to be avoided in academic and scientific settings....
Further reading
- M. Massimini, G. Tononi, et al., "Breakdown of Cortical Effective Connectivity During Sleep," Science, vol. 309, 2005, pp. 2228–32.
- P. Cicogna, V. Natale, M. Occhionero, and M. Bosinelli, "Slow Wave and REM Sleep Mentation," Sleep Research Online, vol. 3, no. 2, 2000, pp. 67–72.
- D. Foulkes et al., "Ego Functions and Dreaming During Sleep Onset," in Charles Tart, ed., Altered States of Consciousness, p. 75.