sleep

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Sleeping child
Sleeping kitten

Sleep is a state of external calm in humans and animals . Many signs of life differ from those of the waking state . The pulse , respiratory rate and blood pressure drop in primates and other higher living beings in so-called NREM sleep and brain activity changes. Closing the eyes during NREM sleep supports this function.

In the so-called REM sleep , also known as “paradoxical sleep”, however, there are states that are similar to those of being awake, in particular increased brain activity ( dreams from this phase are most often remembered) and an increase in heart rate and Respiratory rate and blood pressure. The muscles that are blocked during REM sleep ( atony ) are excluded from this “active sleep state” . As a result, the dreaming does not live out his motor actions experienced in the dream. A separate branch of medicine, somnology (sleep medicine or sleep research) , deals with the disorders and physiology of sleep .

The functions of sleep are only partially understood. What is certain is that humans and many animals must sleep to survive, but the exact reason is still unknown. Sleep deprivation is a common form of torture .

Efforts to document and assess cultural and historical differences and changes in sleeping habits are relatively new . This should one day make it possible to obtain more precise information about the evolutionary causes of sleep.

etymology

The word sleep is common in the Germanic languages. In Gothic the word was sleps , in Old and Middle High German slāf . The Germanic languages English and Dutch use terms from the same root, namely sleep and slaap . The original meaning of the word sleep is to go limp , which in turn is related to the adjective limp .

Various other expressions have emerged from the word sleep that no longer have much to do with sleep itself. So falling asleep is a euphemism for dying , and coitus is called sexual intercourse. A sleepyhead is actually a piece of clothing, but in relation to a person one means - with negative evaluation - someone who often misses important things due to carelessness or slowness.

Sleep in the animal kingdom

A sleeping male two-horned chameleon

Sleep is common in the animal kingdom, but not universal. The Roman scholar Pliny the Elder wrote in his “Naturkunde ( Naturalis historia )”: “The question of how animals sleep does not require an opaque guess. It is obvious that among the land animals all who close their eyes sleep. Even those who question the other animals believe that aquatic animals also sleep, albeit very little. Yes, you can even hear the dolphins and whales snore. ”Today's view is somewhat more differentiated, it is assumed today that most vertebrates (strictly speaking, the superclass of jaws ) go through the same sleep phases as humans. An exception is, for example, the Echidna , an early representative of the mammals, which does not seem to know dream sleep (REM sleep, see below).

Birds also show a sleep pattern similar to humans as soon as they can be sure that the place in the tree that they have chosen is safe from enemies. They cannot fall off the branch or twig, because a specific arrangement of the tendons causes the toes to firmly enclose the twig and get caught by the weight of the bird alone when it sits down. This allows these animals to sleep peacefully, as they do not have to tense any muscles to sit and keep their balance.

Sleep (including dream sleep) is assumed for other animal species such as snakes, lizards and fish. The less developed the species, the more difficult the assessment. It is also becoming increasingly difficult to distinguish (dream) sleep from just resting.

Animals without movable eyelids sleep with their eyes open, e.g. B. crabs, flies, dragonflies, snakes and fish. A sleep-like state was observed even in invertebrates without a central nervous system, such as the mangrove jellyfish.

Half brain sleep

Several animal species have mastered what is known as half - brain sleep . In this sleep state, only one of the hemispheres sleeps while the other remains active. Only one eye is closed so that the surroundings can still be perceived. This ability was first discovered in dolphins , which, as lung breathers in water, is a necessity in order not to drown. Half-brain sleep is also ensured in killer whales . It is interesting that the calves of these species do not sleep at all in the first month of life, which raises certain doubts about the thesis that sleep is essential for the development of the brain. In the vast majority of cases, newborns sleep significantly longer than adult animals. Sea lions and fur seals both know how to sleep. If they are on land, they sleep like land mammals, in the water they switch to half-brain sleep. Temporary half-brain sleep has also been demonstrated in birds. It is believed that a kind of half-brain sleep also exists in humans when they sleep in a strange place.

Sleep duration of different animal species

In animals, both the total duration of sleep and the duration of REM sleep vary greatly from species to species:

Sleep duration of different animal species
Animal species Sleep
in hours
per day 		Share of the
REM phase
in sleep 		Eye position
during
sleep
Little pocket mouse 20.1 16% both closed
Brown bat 19.9 10% both closed
South opossum 19.4 10% both closed
Night monkey 17.0 11% both closed
cat 13.2 26% both closed
Dove 11.9 8th % one eye open sometimes
Domestic chicken 11.8 10% one eye open sometimes
chimpanzee 10.8 15% both closed
dog 10.7 29% both closed
Emperor penguin 10.5 13% one eye open sometimes
Fruit flies 10.0 0% no eyelids
duck 9.1 16% one eye open sometimes
Rabbits 8.7 14% both closed
pig 8.4 26% both closed
Asian elephant 5.3 34% both closed
cow 4.0 19% both closed
horse 2.9 27% both closed
giraffe 1.9 21% both closed

physiology

bedtime

The so-called "internal clock" ( chronobiology ) is, among other things, significantly involved in regulating the sleep-wake rhythm, which is based on the change between day and night (light and dark). The second factor that influences the need for sleep in addition to the day-night change is the time that has passed since the last time you woke up. Research is trying to gather data on optimal time and length of sleep.

The internal clock also adjusts metabolic processes, growth performance and behavior to the daily fluctuations. A disruption of the normal process ( circadian rhythm ) usually occurs during shift work and long-distance flights ( jetlag ).

Induction of sleep

Three brain regions involved in sleep induction, in essence, the reticular formation in the brain stem and two intermediate areas of the brain : the thalamus and the hypothalamus . The reticular formation is known for its function as a signal generator for alertness and belongs to the so-called ascending reticular activation system . The Formatio reticularis exercises its attention and wake-up functions via messenger substances with which it excites the thalamus, the “gateway to consciousness”. These neurotransmitters are norepinephrine and acetylcholine . There are other complex interconnections within the reticular formation . a. with the raphe kernels . With their transmitter serotonin , they have an inhibitory influence on the noradrenergic systems, especially when falling asleep.

When falling asleep, core areas in the brain stem can inhibit the activity of the thalamus in various ways. Another transmitter substance is used, namely γ-aminobutyric acid (GABA). So there are two main ways in which the ascending reticular activation system reaches the thalamus: directly to activate or increase attention and indirectly via inhibitory nerve cells to decrease attention and induce sleep.

In addition, the same core areas in the brain stem have an inhibitory effect on groups of nerve cells in the spinal cord, which leads to a relaxation of the skeletal muscles ( atony ). Not only do people become sleepy, but the tone of their muscles also decreases. For example, when falling asleep while sitting, the head falls forward. Often times when falling asleep there is also a special jolting to sleep .

The hypothalamus is connected to the eye and produces less of the transmitter histamine and a peptide called orexin (from Greek ὄρεξις orexis "desire, appetite"), which leads to increased alertness . Orexin has a significant influence on the sleep-wake behavior of humans. First the appetite-increasing effects of the hormone were found, hence the name. The nucleus preopticus ventrolateralis (the "eating center of the brain", English ventrolateral preoptic nucleus , VLPO) of the hypothalamus is involved in the induction of sleep. The suprachiasmatic nucleus (SCN) contains direct afferents (feed lines) from the retina . This is where the main control center of the internal clock is located , a kind of "pacemaker" that synchronizes the circadian rhythm . The SCN also affects sympathetic activity . Via this vegetative system , the SCN stimulates the release of melatonin from the pineal gland . Melatonin is increasingly released in the evenings and helps induce sleep. As a result, the hypothalamus tells the brain that it is time to sleep because it has become dark.

The body has other messenger substances that can contribute to an increased need for sleep. During high metabolic activities (physical work), more adenosine is produced , which causes fatigue . Also inflammatory mediators such as interleukin-1 have a similar effect and result in an accompanied by fever disease to an increased need for sleep.

Maintaining sleep and phases of sleep

Representation of the sleep stages in the hypnogram of one night according to Rechtschaffen and Kales (1968)
Hypnogram of a 90-minute sleep cycle - after a short “lying awake” (W), some light sleep (N1) followed, interrupted by waking up again, then some sleep of stage N2 and extensive deep sleep (N3) as well as 13 minutes of REM sleep (R ). According to the classification of sleep stages that has been in effect since 2007 .

Sleep is also controlled neurophysiologically in its further course. To maintain it, functional systems of the brain vary the depth of sleep at time intervals. Deep sleep phases, in which the sleeper is more difficult to wake up, alternate with less deep sleep. If towards the end of sleep, usually after about six to eight hours, these phases of sleep alternate at ever shorter intervals, the sleeper wakes up. This cyclical process is also called the sleep rhythm .

During healthy sleep, associations of nerve cells show special synchronizations. This means that their action potentials are triggered in a common rhythm. By deriving electrical voltage fluctuations on the head surface by means of electroencephalography (EEG), these different rhythms can be measured and made visible. Depending on the depth of sleep and the associated characteristic wave pattern, sleep can be divided into different stages. According to the frequency and amplitude of these "inner rhythms", the following stages and the associated waves are distinguished, whereby the following division of sleep stages I-IV is from 1968 (in the more recent division from 2007 the two deep sleep stages 3 & 4 are one, N3, summarized; see sleep profile ):

  • Attention: beta waves (14 to 30 Hz),
  • relaxed with eyes closed: alpha waves (8 to 13 Hz),
  • Stage I (light sleep, shortly after falling asleep): The brain changes from alpha waves to theta waves (4 to 7 Hz). The muscle tension is reduced and the conscious awareness of the environment slowly disappears.
  • Stage II: In this phase, theta waves continue to occur, so-called sleep spindles and K-complexes are added . This sleep stage becomes increasingly longer in the course of an 8-hour sleep and takes up more than 50 percent of the total sleep.
  • Stage III (transition to deep sleep): Delta waves (0.1 to <4 Hz - slow waves with high amplitude) now come to the fore (20 to 50 percent of the measured brain waves), the muscle tension continues to decrease.
  • Stage IV (deep sleep): Delta waves now make up more than 50 percent of the measured brain waves. It is the deepest phase of sleep, and sleepers who are now woken up appear disoriented and sleepy. In this phase of sleep, however, phenomena such as sleepwalking and speaking while sleeping occur.
  • REM sleep: The so-called REM sleep ( rapid eye movement, also dream sleep or paradoxical sleep ) differs in many ways from the other sleep phases. The EEG is similar to sleep stage I (predominantly theta waves). However, there are fast, directionless movements of the eyeball at regular intervals with a frequency of 1 to 4 Hz. Dream reports from awakenings in this phase are significantly more vivid, visual and emotional than with awakenings in other phases. During REM sleep, the skeletal muscles are maximally relaxed , but not the eye muscles. Most of the vegetative functions are activated with an increase in blood pressure, respiratory and heart rate, as well as increased blood flow to the genitals. The latter manifests itself as an erection in men . The stress hormone adrenaline is released more in this phase (possibly more heart attacks in this phase) and gastric and duodenal activity increases. The duration of the individual REM phases is an average of five to ten minutes at the beginning of night sleep and becomes longer in the following phases. The average total time per night for adults is approx. 104 minutes. In contrast, fetuses and newborns spend almost the entire duration of their sleep in REM sleep. There appears to be a clear connection between REM sleep and CNS maturation . The function of this sleep phase is the subject of intensive research.

  • Stage I.

  • Stage II, sleep spindles are underlined in red.

  • Stage IV

  • REM sleep

Stages I-IV (in contrast to REM sleep) are referred to as non-REM , NREM or orthodox sleep . Stages III and IV are referred to as deep sleep or (due to the slow brain waves) slow wave sleep . In stages I to IV, EMG activity ( electromyography ; muscle tone , especially of the neck and neck muscles) decreases until complete muscle atony occurs during REM sleep . Stages I to IV followed by REM sleep are repeated several times per night (about five to seven times). The phases of deep sleep decrease over time and the REM phases increase. Stage IV is no longer reached later in the night. Older people very often no longer reach stage IV at all. The sleep pattern also changes with age: old people sleep only a few hours at night and often sleep another one or two hours a day. Infants sleep all day, but in short phases. In adults, sleep is focused on a core time, usually at night. A sleep cycle lasts about 90 minutes. This 90-minute cycle continues when you are awake and leads to phases of changing willingness to perform ( ultradian rhythm ).

Variations in sleep duration in humans

The “optimal” daily amount of sleep for humans, which is subject to individual fluctuations, as well as its distribution over the day is scientifically controversial. After the negative consequences of lack of sleep were the focus of research for a long time, the apparently equally unpleasant consequences of too much sleep have recently come to the fore. According to large studies in the USA and Japan, it seems to be emerging that the "eight hours a day" often mentioned for adults are already too long and the optimum is between six and seven hours, which is also the average sleep time Germany corresponds to (6 hours 59 minutes according to a study carried out at the University of Regensburg ). Studies by the universities of Warwick and London came to the same conclusion. An international study by the American National Sleep Foundation in 2013 also showed comparable results, with clear differences in the length of sleep between working days and days off. Most people also said they did not get as much sleep as they would need to feel relaxed. Even so, the majority said they got enough sleep on weekdays to feel refreshed in the morning. A study published in Current Biology with 33 participants suggests a possible connection between sleep structure and the phases of the moon .

Individual differences

The adult's individual need for sleep fluctuates between six and ten hours and follows a roughly normal distribution . Extremes occur in infants who sleep 14 to 17 hours (spread over the day) and in old people whose need for sleep is less (“ senile bed escape ”). According to the sleep researcher Peretz Lavie , a person with healthy sleep can be assumed if he or she feels comfortable with a daily sleep of four to twelve hours.

Age-related average sleep requirement per day in humans
Age Average sleep requirement in hours / day
0-3 months 14-17
4-11 months 12-15
1-2 years 11-14
3-5 years 10-13
6–13 years 9-11
14-17 years 8-10
18–64 years 7-9
over 64 years 7-8

It is of crucial importance that the individual, differently pronounced need for sleep is constitutionally prescribed and consequently cannot be switched off or ignored in the long term through misunderstood "training" without harming the organism. Anyone who is one of those people with an increased need for sleep should therefore adjust their daily rhythm of life accordingly and adapt their behavior accordingly. The optimal length of sleep for a person also depends on the circadian rhythm . Because sleeping at the "wrong" time of day is relatively inefficient. The period for sleep is best when the following two events coincide in the middle of sleep:

Furthermore, within a 24-hour day, the phases of maximum and minimum performance are distributed differently depending on the type. To simplify matters , a distinction can be made between a morning type and an evening type. The morning type (for example an early riser) is fit and productive early in the morning, the evening type , among other things, as a night owl (also night owl ) develops a maximum of activity in the late evening. In 2005 the long-known genetic influences that play a role in this were specified (Period3 gene).

Daytime sleep is possible because the hormone release only begins after the induction of sleep. If you wake up shortly after sleep has started, you may have completed an REM phase, but not yet have such a high hormone concentration that you would fall asleep again immediately.

lack of sleep

Sleep deprivation is the cumulative effect of not getting enough sleep. Lack of sleep can lead to mental or physical fatigue and reduce performance accordingly. The exact physiological changes caused by lack of sleep are the subject of research.

Excessive tiredness during the day can be a result of lack of sleep. However, it can also be a result of a sleep disorder such as narcolepsy or sleep apnea syndrome. An affected person is always tired, even if they have slept long enough. These symptoms should be discussed with a doctor. The diseases are often treatable. Those who are not aware of these diseases can become a danger to themselves or others, for example through microsleep while driving or sudden inattentiveness at work. Sleep doctors call this clinical picture "non-restful sleep". Excessive tiredness despite getting enough sleep can be due to iron deficiency, anemia or other deficiency symptoms, especially in young women .

Turning the radio up while driving, opening the window or turning on the air conditioning to stay awake only helps for a short time and can be dangerous for the person if you continue to drive despite being tired or dizzy. Anyone who feels tired while driving should stop and rest as soon as possible. Caffeinated drinks only delay tiredness. According to Spork (Das Schlafbuch, 2007) , the most effective way to help is to go to a parking lot immediately, drink a strong caffeinated drink, and then sleep. The caffeine wakes the person after about 30 minutes and studies have shown that it is possible to continue driving without an accident. The combination of sleep and caffeine worked better in the studies than either of the measures alone.

Sleep disorders can often occur in the context of mental disorders and illnesses, for example depression, anxiety disorders or psychoses. However, sleep disorders can also be the cause of the later occurrence of mental illnesses, particularly depression.

In adolescents, the duration of sleep decreases significantly compared to childhood. Youngsters in grade 12 sleep an average of 6.9 hours per night. Restful sleep is important for e.g. B. Feeling, thinking and social interaction. A lack of sleep in adolescence can manifest itself, for example, in a bad mood and poor emotion regulation. Lack of sleep also increases the likelihood of risky behavior, such as B. Drunk driving or drug use among adolescents.

Long-term lack of sleep without adequate recovery periods can have negative effects on mental and / or physical health. Possible consequences can be circulatory problems such as B. high blood pressure or circulatory disorders. In addition, lack of sleep can promote depression and is more common with the same.

function

The elucidation of the biological functions of sleep is still the subject of intensive research. However, there are already a number of hypotheses, some of which have already been substantiated quite well by psychological and physiological experiments.

evolution

The earth's rotation, with its rhythm of day and night , provided the basis for the development of rest and activity cycles. The flowers of plants open and close depending on the time of day. Even single-celled organisms such as the flagella Lingulodinium polyedrum (= Gonyaulax polyedra ) adjust their activity according to the position of the sun . Such observations on underdeveloped organisms suggest that adaptations to light and temperature conditions took place early in evolution in order to regulate metabolic activity . Staedt and Stoppe suspected in more recent studies that the electrophysiologically measurable sleep had developed in the course of the development of increasingly complex neural networks . According to this, there would be a direct relationship between the need for sleep and the performance of the brain, especially with regard to the processing and storage of information.

Developmental biology

Developmental observations showed that the processes during REM sleep in newborns seem to be particularly important for the development of the young organism. Studies examining the effect of lack of sleep in young children have shown that this leads to behavioral disorders, permanent sleep problems, reduced brain mass, and abnormally high nerve cell mortality.

REM sleep appears to be critical to brain development . In newborns - who are already sleeping a lot - it makes up most of the sleep. If you compare different animal species, the deep sleep phase of newborns is longer, the less developed the baby is born. It has been suggested that during REM sleep the muscles would be partially paralyzed in order to stimulate the activation and development of the brain without the resulting nerve impulses leading to movements that could cause difficulties in particular for a newborn. REM deficiency in young children leads to developmental problems later.

However, this theory does not explain why adults still need REM sleep, and it does not explain enough, which is why the REM percentage is about the same as in an adult after the age of three. The cubs of marine mammals do not have REM sleep at the beginning of their life; it only increases over time. At least in these animals it is not necessary for development. It should be noted, however, that these animals can never sleep with both halves of the brain, otherwise they would drown as lung breathers.

Removal of waste from the brain

Through the filter systems of the blood-brain barrier and the blood-liquor barrier , both the supply (nutrients) and the disposal (waste materials) of the brain and spinal cord (CNS) are actively restricted and under special biochemical and biophysical control. However, since there is an unusually high average metabolism here , special facilities must be available in order to guarantee the necessary transport to and from the plant.

Research into these relationships led to the discovery of the glymphatic system in 2012, a special microcircuit in the CNS for flushing out superfluous and harmful material.

The comparison of the transport in awake and sleeping animals showed a decrease of about 95% in the awake state. It was also shown that the volume of the cell space (interstitium) increased during sleep due to the shrinkage of the cell bodies, with a share of the total volume of around 24% compared to around 14% in the waking state. During sleep there was therefore> 60% more space for fluid transport. Norepinephrine , a main modulator of wakefulness, has also proven to be a possible regulator of the volume of the intercellular space and thus of the effectiveness of the glymphatic system .

This disposal system has been the subject of intensive research since then, in particular because of its importance for the development and prevention of neurodegenerative diseases such as Alzheimer's disease , Parkinson's disease or amyotrophic lateral sclerosis (ALS).

regeneration

Girl who fell asleep while knitting (Tricoteuse endormie) by Jean-Baptiste Greuze (1724–1805). Oil on canvas, 64.3 × 51 cm.

Sleep promotes wound healing . A study by Gumustekin in 2004 was able to show that sleep deprivation the healing of burns adversely affected in rats.

Sleep deprivation has also been shown to affect the immune system and metabolism . In one experiment, rats were prevented from sleeping for 24 hours. Compared to the control group, the proportion of white blood cells was reduced by 20 percent, which is a clear change in the immune system.

Healthy people have a significantly higher metabolic rate than people who suffer from a sleep disorder.

A study of 305 children collected information on growth, height and weight, as well as the sleep time recorded by their parents during the first ten years of life. The study found no discernible association between length of sleep in children and their growth. However, the concentration of growth hormones increased in adult men during sleep, especially in stages III and IV. During a sleep time of eight hours, especially those men released a lot of growth hormones whose entire deep sleep phases were relatively long. However, it is still unclear whether natural or unnatural changes in sleep duration lead to differences in growth.

The sleep time of different species is generally inversely proportional to the size of the animal, but increasingly with the basal metabolic rate , which is large in small animals (see also Kleiber's law ). Rats with a very high basal metabolic rate sleep up to 14 hours a day, while elephants and giraffes with a significantly lower turnover only sleep three to four hours a day.

To save energy, it would be sufficient to rest motionless without cutting off part of the organism from the environment , which can be dangerous. A resting, but not sleeping, animal has a better chance of avoiding predators and can still conserve energy. However, studies on humans have shown that test subjects actually consume significantly more energy when they are awake, despite physical inactivity, than when they are sleeping or in the same period (24 hours) with a normal sleep-wake rhythm: during the night when the effect is particularly pronounced, the test subjects showed almost a third (~ 32 percent) higher energy consumption when they were awake than when they were asleep. Recent studies have shown that not only does sleep lead to energy savings, but v. a. In some areas of the brain during deep sleep, this leads to significant energy storage. The universal energy carrier ATP ( adenosine triphosphate ) increased in the brain of rats only during deep sleep and was related to the decrease in nerve activity in this sleep stage. The same could be shown in studies with anesthetized animals.

Some animals need another rest after waking up from their hibernation , possibly due to "lack of sleep" during hibernation. The animals had enough rest here, but apparently need sleep for something else.

Order, sort out and consolidate memories

According to this hypothesis, experiences of the waking phases are processed during sleep. The brain is "cleaned" of superfluous information. Sleep also helps to classify positive and negative experiences (“I have to sleep over that first”), including in the form of dreams.

Scientists have discovered several links between sleep and memory . The researchers allowed 18 women and 22 men to sleep just 26 minutes a night for four days. During the test phase, cognition and memory tests were continuously carried out on the subjects. In the last test, the amount of working memory was 38 percent less than a comparison group who slept normally. It was shown that the performance of working memory with lack of sleep suffers. Working memory is important because it provides information for further use in a current situation at short notice and thus makes an important contribution to decision-making .

Memory seems to be affected differently during different phases of sleep. In a study in which several groups of people were awakened at different times, it was shown that declarative memory is mainly promoted by deep sleep, but procedural memory is mainly promoted by a long REM sleep phase.

Further investigation indirectly supported these theses. The subjects were 22 male rats. In a cage, a single rat could roam freely from one end to the other. The bottom of the box was made of a steel mesh. A beam of light illuminated the box and a loud signal sounded at the same time. Five seconds later, the rats were shocked with electric batons. If a rat went to the other end of the box, the shocks stopped. If she was fast enough, she could even avoid it completely. The test was carried out 30 times on half of the rats, while the remaining rats (as a control group) were treated with electric shocks regardless of their reaction. After each test phase, the rats were placed in a detector for six hours, which collected brain waves, sleep stages and other data on the animals. The test was repeated three times in total. The study concluded that while sleeping after the tests, those rats that had learned had about 25 percent longer REM sleep than the control group that had learned nothing. This research supports the aforementioned results and shows a correlation between REM sleep and procedural memory.

In the meantime, the strengthening of nerve connections that served special memory contents could be observed directly during sleep with the aid of optogenetics . Furthermore, if sleep was interrupted by disturbance, the strengthening of nerve connections was also interrupted.

In 2015, it was possible for the first time to create an artificial (false) memory in mice during sleep, which the animals then immediately confirmed through their behavior after waking up. A place cell in the brain region for spatial memory ( hippocampus ) was linked by electrical stimuli to a brain region ( nucleus accumbens ) that is central to pleasant feelings during sleep . After waking up, the animals visited the corresponding place of their dwelling with noticeable frequency, just like other animals that had learned a real memory of the place while they were awake.

Synaptic homeostasis hypothesis

Giulio Tononi , in collaboration with Chiara Cirelli, developed the synaptic homeostasis hypothesis, which states that deep sleep is necessary to restore a basic level of synaptic interconnection: in the waking state, reinforcements in the network structures of the nerve cells are formed due to the increased flow of information , i.e. H. the strength of the synapses increases, and synaptic new connections are also created. This happens through the known mechanism of long-term potentiation : Certain combinations of signal transmissions between nerve cells cause the synapses involved to potentiate, which lasts for a longer period of time. If these processes were to continue unhindered over time, the networks would soon be overloaded. In deep sleep (more precisely: in non-REM sleep ) there is a kind of synchronization of certain neuronal groups, which is noticeable through slow-wave potentials ( so-called delta waves appear in the EEG ) and lead to the synaptic bond strengthens and also the number of synapses decrease again (synaptic downscaling). Only the “strong” synapses remained. The regression of the synapses caused in deep sleep should provide enough energy and space for new learning and processing processes due to the selective reduction. It is also assumed that important things can be separated from unimportant things and filtered out within the given wealth of information.

"Essentially, sleep is the price we have to pay for neural plasticity ..."

- G. Tononi and C. Cirelli

In contrast, Jan Born pointed out that some of the nerve connections newly formed during the day would be spared from the general nocturnal weakness. These permanent new connections represented new memory contents, which would be reinforced at night by the fact that other - less important - connections of a common network would be weakened. Tononi has now also integrated this component into his theory.

Problem solving while sleeping

The everyday experience that some problems suddenly resolve themselves when you wake up in the morning has been scientifically confirmed since 2004 repeatedly in sophisticated experiments. Test subjects solved number puzzles that required several individual steps. What they weren't told was that there was a shortcut that could save you a few steps. After the practice phase, some of the subjects were allowed to sleep for eight hours. According to this, more than twice as many test persons in this group were aware of the possibility of shortcuts as in the groups who had stayed awake for eight hours during the day or night.

Box with alternating light-up push buttons

Another experiment compared problem solving while sleeping between a group of 11 year old children and their parents' group. With a box with several buttons, the ones that were lit up had to be pressed as quickly as possible. What was not said was that there was a regularity in the order of lighting up. After an initial phase of practice, when asked, none of the children or adults noticed anything about the regularity. When the experiment was repeated with new test subjects and this time there was a sleep phase between the exercise phase and the inquiry, some adults and almost all children were aware of the regularity and were able to fully reconstruct the previously unknown sequence.

Sleep research

Historical beginnings

The sleep research is a relatively new discipline in biology and medicine, the first electroencephalography -Untersuchungen (EEG) in the sleep laboratory were made in the 1920s. The Greek physician Hippocrates and the philosophers Plato and Aristotle had tried to explain sleep by the rising of poisonous vapors in the stomach that were ingested with food, which would be broken down during sleep. In addition, blood that is said to have become overheated, dammed or thickened while waking can only be cooled and thinned while sleeping. In the Middle Ages, the naturopath Hildegard von Bingen thought that people needed sleep because they basically consist of two parts. That is why being awake needs the opposite pole of sleep. In the 19th century, Alexander von Humboldt still assumed that sleep was necessary in order to counteract an oxygen deficiency in the brain.

The researchers Eugene Aserinsky and Nathaniel Kleitman made the important discovery of REM sleep in 1953. Four years later, the theory was put forward that dreaming only takes place during this phase of sleep. This has been refuted today, because one clearly dreams in deep sleep, but one still assumes that dreams in REM sleep are particularly realistic and vivid.

Sleep research in sport

Everything that affects or promotes athletic performance is researched within the framework of training science. Since athletes often have to compete on consecutive days, sleep research is an important sub-discipline. Because melatonin does not interfere with physical performance, it is the first choice aid for jet lag. In competitions, however, it is often a question of the interaction between rapid recovery and sleep. A dinner high in carbohydrates is good for replenishing glycogen stores , but it causes a shorter sleep, whereas a dinner high in protein is not only good for sore muscles , but also improves the quality of sleep. Fat with dinner negatively affects the total length of sleep. If the amount of calories is reduced, the sleep time is shortened. See also obesity # sleep habits .

Sleep and sexuality

connotation

The expression "sleeping together" stands for sexual cohabitation. In fact, the sexual intercourse practiced while awake has nothing to do with sleep in the strict sense of the word. The origin of this description may come from the fact that the usual place for sexual intercourse, as for "normal" sleep, is the bed. In Japan, for example, after the Second World War, during the occupation by the Americans, even the imaging and filming of bedrooms was forbidden for moral reasons. The Japanese associate everything that has to do with sleeping places with sex, even more than the Europeans, such as the expression “sharing the pillow” or the “mat made of rice straw” ( tatami ).

Pollution

Pollution or nocturnal ejaculation is an involuntary ejaculation , triggered by an unconscious orgasm , which can occur without active involvement and without wakefulness in men and male adolescents from puberty during sleep. This event is often accompanied by erotic dreams.

Morning erection

A morning erection is an erection of the penis that is noticed when you wake up in the morning. Some men have an erection almost every morning, others rarely or never. The cause of this particular erection is not suspected to be sexual arousal , but rather in circumstances accompanying the REM phase of sleep. During the REM phases, the pulse and breathing accelerate and the sleeper experiences intense dreams. Apart from nightmares , erections are also common during these phases. These erections are independent of whether the dream content is sexual or not.

Sleep and study

Healthy sleep is essential for optimal memory function. Sleep, learning, and memory are complex, interacting phenomena. Many studies in humans and animals indicate that the quality and quantity of sleep has a great effect on learning and memory function. According to the current state of research, sleep promotes learning and memory in two different ways. First, a sleep-deprived person lacks the ability to concentrate to absorb new information and thus cannot learn effectively. Second, lack of sleep disrupts the consolidation and integration of what has been learned.

Pathology of Sleep

In medicine, pathology is the term used to describe the "theory of abnormal and pathological processes and conditions in the body and their causes". (See also insomnia )

Sleep apnea

Sleep apnea syndrome (SAS) is a symptom that is usually caused by respiratory arrest (apnea) during sleep and is primarily characterized by pronounced daytime sleepiness up to the need to fall asleep ( microsleep ) as well as a number of other symptoms and secondary diseases.

The respiratory arrests lead to a reduced oxygen supply and repeated wake-up reactions (as an alarm reaction of the body). Most wake-up reactions do not lead to waking up, but only to increased body functions, for example an accelerated pulse. That is why they are usually not noticed by those affected. As a result of the wake-up reactions, the restfulness of sleep is lost, which usually leads to the typical, pronounced daytime sleepiness.

Restless legs syndrome

In restless legs syndrome (Wittmaack-Ekbom syndrome), patients suffer from unpleasant sensations or the urge to move in the legs (or arms) as soon as they come to rest so that they cannot fall asleep at night. RLS is a neurological disease that is very widespread (five to ten percent of the population). It is often not recognized as the cause of the sleep disorders for a long time - even by those affected themselves . The resulting sleep deprivation through the disturbed sleep phases leads to daytime sleepiness, cognitive performance losses and depressive moods. Treatment with medication is almost always possible.

Circadian sleep-wake rhythm disorder

These disorders are sleep disorders in which those affected have an atypical biorhythm. The sleep phase is shifted accordingly, which can lead to problems with social norms that apply to working hours, for example.

With delayed sleep phase syndrome (also called delayed sleep phase syndrome, DSPS) and advanced sleep phase syndrome (also called advanced sleep phase syndrome, ASPS), those affected are unable to get used to a sleep-wake rhythm that suits them. With delayed sleep phase syndrome it is only possible for you to find sleep late in the day - i.e. early in the morning - or with advanced sleep phase syndrome at an early time - i.e. in the afternoon or early evening.

A sleep-wake disorder that deviates from the 24-hour rhythm causes those affected to fall asleep at a different time each day. An interval between sleeping and waking is then either shorter than 24 hours, so that those affected fall asleep earlier each day and accordingly wake up earlier, or it is longer than 24 hours so that those affected fall asleep later each day and accordingly wake up later.

Narcolepsy

Narcolepsy is a syndrome of four characteristic areas, the predominant symptom of which is a pathologically increased daytime sleepiness in connection with a changed phase structure of night sleep. In addition, there is often a loss of muscle control ( cataplexy ) and / or correspondingly induced sleep (trigger sleep) during the day caused by trigger events . In connection with the changed order of the nocturnal sleep phases, hypnagogic hallucinations and sleep paralysis can also occur.

Sleep paralysis sometimes occurs upon awakening, even in healthy people. The nerve block is then loosened in the wrong order, so that first the sensory nerves and then the motor nerves are “released”. In this state, the person concerned sees, hears and feels everything, but cannot say anything, cannot move, and cannot accelerate breathing. An intense feeling of total powerlessness is reported.

A similar condition sometimes occurs in under- anesthetized patients during surgery. Some forms of coma are also said to be felt by those affected, and there have also been reports from drug users about such experiences.

Fatal familial insomnia

The fatal familial insomnia is a disease in which those affected are unable to sleep. This disease is an extremely rare familial disease . A mutated prion protein gene is responsible for the disease . Most patients become ill between the ages of 40 and 60. The focus is on a severe disruption of the patient's sleep-wake rhythm, i.e. they suffer from severe sleep disorders . It is therefore assumed that the pathological changes take place specifically in the brain stem, which, as an evolutionarily old part of the brain, controls the rhythm of activity. The disease lasts seven to eighteen months and has always been fatal. It was first described in 1986 and its hereditary transferability was proven in 1995.

Bruxism

Bruxism is the technical term for mostly nocturnal teeth grinding that the person concerned is not aware of. It is usually recognized by dentists on the basis of ground teeth. A mostly soft splint, which is mainly worn at night, protects the teeth.

treatment

There are recommendations to counter insomnia with sleep rituals: evening prayers, breathing techniques, pulsating light, “counting sheep” and so on help the psyche to calm down through familiar thoughts. Barmer health insurance recommends masturbation to help you fall asleep. However, people experience insomnia in various circumstances, such as reactive depression or the disorder of pain . In these circumstances, sleeping pills (hypnotics) can be used.

Furthermore, it is recommended to observe the most important rules of sleep hygiene, i.e. to keep a regular sleep rhythm.

In addition to herbal medicines ( e.g. valerian ), antihistamines , short-acting benzodiazepines ( e.g. brotizolam ) as sleep aids, medium-acting benzodiazepines ( e.g. nitrazepam and diazepam ) as sleep aids and newer short-acting sleep aids such as zopiclone and zolpidem are used to treat sleep disorders . Antihistamines mediate their effects by inhibiting the action of the "waking hormone" histamine on its histamine receptors . Benzodiazepines, zolpidem and zopiclone act on the GABA receptors in the thalamus. There they promote the inhibitory effect of this transmitter. The barbiturates , which used to be very common, are now practically no longer used as a sleep aid due to an unfavorable risk-benefit ratio ( suicide potential and suppression of REM sleep).

In the US, the hormone melatonin , which is physiologically released from the pineal gland , is increasingly being sold as a miracle drug and anti-aging agent. It is known that melatonin has sedating properties and that its production increases more and more in the evening hours, making it a kind of endogenous sleeping aid. However, the use of melatonin as a drug is controversial.

sleep deprivation

Sleep deprivation is the intentional or unintentional prevention of sleep, i. H. the suppression of sleep pressure.

Therapeutic sleep deprivation

In psychiatry , therapeutic sleep deprivation is used in the treatment of depression . In about 60% of the patients there is a temporary improvement in symptoms after a sleepless night. However, the antidepressant effect is usually not sustained, so most patients would relapse even after a night of sleep (a so-called rest night). However, up to 15% of patients in clinical trials show a sustained response after total sleep deprivation.

consequences

Persistent sleep deprivation for seven days led to death in rats due to skin ulcers , polyphagia with simultaneous weight loss, and a decrease in body temperature, sometimes in connection with blood poisoning . Before she died , her body temperature ( thermoregulation ) and weight dropped .

The world record in sleep deprivation was set in 2007 by British Tony Wright. He didn't sleep for 266 hours. He broke the record of the 17-year-old American student Randy Gardner from 1965, who spent 264 hours (exactly eleven days) without sleep. However, Wright was not interested in an entry in the Guinness book like the American Gardner , but wanted to show that a person can remain productive despite sleep deprivation with the right diet. However, experts like the US sleep researcher William Dement doubt that people can stay awake that long at all. Micro-sleep episodes and microsleep attacks are likely to have occurred repeatedly during the records.

Sleep deprivation as torture or punishment

Sleep deprivation was and is used as a torture device .

In ancient Rome , King Perseus of Macedon is said to have been killed as a prisoner by being deprived of sleep. It is reported from ancient China that criminals were punished with death by being deprived of sleep.

In the prison camp operated by the USA near Guantánamo , attempts are often made to persuade prisoners to cooperate by depriving them of sleep during interrogations.

In the Federal Republic of Germany were RAF detainees, in solitary confinement prevented in cells with continuous illumination and by regularly wake the sleeping. In the Soviet Union under Stalin , sleep deprivation was a common interrogation method , but also in the GDR in Stasi prisons until 1989.

Sleep deprivation from stimulants

Various substances can be used to suppress the need for sleep. The active ingredient caffeine is known for its wakefulness-promoting and stimulating effect , which is contained in coffee , for example, and also in tea in a mostly lower concentration . Caffeine acts in the central nervous system primarily as adenosine - antagonist . The caffeine helps fight the drop in respiratory rate, especially in older people .

Drugs of the (indirect) sympathomimetic type , such as amphetamine , ephedrine or cathine (from the Kath leaves), have a stimulating effect - with considerable side effects. The neurostimulants modafinil and methylphenidate , as well as off-label amphetamine , are used against obsessive-compulsive sleepiness, as occurs in narcolepsy .

dream

Pierre Puvis de Chavannes , The Dream , 1883

The psychological experience in sleep, which is predominantly characterized by sensory perception, is called a dream. Cognitive skills such as conceptual thinking and causal- logical remembering take a back seat. During the dream event, a distinction between psychological experience and physical sensory perception is abolished, as a result of which internal psychological processes are experienced as external physical reality. Most dreams are often difficult or impossible to remember when you wake up. However, studies show that people almost always remember vivid dreams when waking up straight from REM. In the REM stage, the brain is as active as when falling asleep, so this is also an optimal time to wake up.

Only in rare cases does the sleeper experience a lucid dream, that is, he is fully aware that he is dreaming and can actively influence his actions in the dream. Dream memory can also be trained. This approach is often undertaken by people who want to experience more lucid dreams.

The dream interpretation is also called oneirology in scientific and extra-scientific areas .

snoring

While snoring might be harmless to most people, it could be an indication of a life-threatening sleep disorder called sleep apnea syndrome , especially if it is accompanied by great daytime tiredness. The sleep apnea sufferer breathes intermittently, which can lead to a lack of oxygen. People suffering from it wake up at night and pant for air. Breathing pauses reduce the amount of oxygen in the blood, stress the heart and blood circulation and can lead to cardiovascular diseases .

Sleep culture

The sleep culture describes cultural and historical aspects of sleep. When, where and how people go to sleep in different places and at different times are part of the sleep culture.

Because sleep and everything related to it is generally viewed as a very personal and intimate affair, research and records on the subject are rare. Scientific work that tries to draw conclusions about the evolutionary causes of sleep on the basis of the sleeping habits of different peoples, especially those who live very close to nature, has only recently been undertaken.

Sleep in the fine arts

Sleep with its various aspects has been taken up by many artists. The sheltered sleep of children, sleeping animals, the afternoon nap and falling asleep at work, daydreams, dreams and nightmares, sleep and death, sleep and the naked human body as a classic subject of the visual arts have been used as painting, drawing and graphics, and also implemented as sculptures and sculptures.

  • A nap in art. Vincent van Gogh ("La Méridienne" or "La sieste", after Millet, January 1890)

  • Four people in the train compartment, two asleep, one dozing, each in a world of its own. Honoré Daumier ("The Second Class Carriage", 1864)

  • Woman pretending to be asleep. Vito D'Ancona (Nudo, before 1884)

  • Naked sleeping, dying man. Pierre-Narcisse Guérin (Aurora and Cephalus, 1783)

  • Sleeping girl. Albert Anker (sleeping girl on a wooden bench, date unknown)

  • Sleeping girl. Anna Rajecka (girl with straw hat)

  • Sleepy girl. Jean-Baptiste Santerre (A Sleeping Girl, 1700–1725)

  • Sleeping boy. Albert Anker (Sleeping Boy in the Hay, 1897)

  • Sleeping animal. (Paul Klimsch, Sleeping Jaguar)

  • Sculpture of sleeping woman in Kolonistsky Park in Peterhof

  • The artist's wife sleeping in the armchair. Ilya Repin (rest, 1882)

  • Venus and Cupid. Marie-Françoise-Constance Mayer-La Martinière (The Sleep of Venus and Cupid, 1806)

  • Two sleeping women. George Hare (Victories of Faith, 1889)

  • Goya dreaming. Francisco de Goya ( The sleep of reason gives birth to monsters , 1799)

reception

  • In the science fiction series Star Trek: Voyager , people encounter an alien life form called Species 8472 that never rests and finds sleep strange. The necessity of sleep, which people take for granted, is contrasted in this context with the fiction of a sleepless way of life.
  • In Robert Schneider's novel Schlafes Bruder , the protagonist commits suicide by vowing to never sleep again.
  • In the film The Machinist , the protagonist has not slept for about a year.
  • In the movie Die Another Day in the James Bond series, Bond's opponents Colonel Moon and Zao undergo gene therapy to change their identities. However, the side effect is persistent insomnia, which they try to avoid with the help of a “dream machine”. Those affected find it a great agony not to be able to sleep properly. The public, however, is bragged about not needing sleep and thus being able to do more: after all, you can get enough sleep when you are dead.
  • In the award-winning science fiction novel Beggars in Spain by Nancy Kress , which was later expanded into a trilogy, insomnia is also associated with elite and intellectual superiority: Through Genetic Modification children are created, which are characterized by high intelligence, immunity against diseases and insomnia. In the further course of the plot u. a. the social conflict between this new elite of the insomniacs and the old people, the sleepers , is a theme.
  • In the novel Sleepless by the book author Stephen King , the main character of Ralph Robert suffers from an extreme form of insomnia. As a result of the ongoing sleep deprivation he is haunted by phenomena which he initially regards as hallucinations; Later, however, he finds out that the lack of sleep has apparently changed his sensory perception.
  • In the novel The Moor ghost of Angela Sommer-Bodenburg the young Timo meets an old man in the car. This tells him about the dealer of the sold dreams. By trading with this he suffers from insomnia (“can no longer dream”) and has been traveling by train since then until he finds the dealer again in order to reclaim his dreams. At the end of the novel, Timo suspects that the man was a ghost.
  • In the novel Fight Club by Chuck Palahniuk the unnamed narrator suffers from insomnia.
  • In the novel, as well as in the movie 2001: A Space Odyssey by Stanley Kubrick astronauts for the time of the flight to Jupiter (film) respectively Saturn (Roman) are put into a deep sleep. The devices for this are called hibernaculum, which people hibernate .

See also

literature

swell

Further information

  • Émile Chartier : Les idées et les âges. 1927. German: Age and view. Berlin / Vienna / Leipzig 1932. The first book of this philosophical work is explicitly devoted to sleep, also reaching out in terms of cultural history. Besides sleep, night and the like Similarly, the Frenchman, also known as Alain, considers the important social role of the guard.
  • Sonja Kinzler: The yoke of sleep. The sleep discourse in the bourgeois age. Dissertation at the International University Bremen 2005. Böhlau, Cologne / Weimar / Vienna 2011, ISBN 978-3-412-20716-8 .

Web links

Commons : Sleep  - Collection of pictures, videos and audio files
Wiktionary: Sleep  - explanations of meanings, word origins, synonyms, translations
Wikiquote: Sleep  Quotes

Individual evidence

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  84. ↑ FBI : A Review of the FBI's Involvement in and Observations of Detainee Interrogations in Guantanamo Bay, Afghanistan, and Iraq (PDF; 6.4 MB) p. 182 ff.
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This version was added to the list of articles worth reading on December 4, 2005 .