Sleep Nature: why we sleep and how we are affected by lack of sleep

Why do we sleep

Specializing in sleep psychiatrist Allan Hobson (Allan Hobson) once joked that the only known function of sleep - the treatment of sleepiness. That's not quite true, but the question is why this process is so necessary, has not been solved until the end.

It remains unclear why the dream as an evolutionary strategy even came into being. After all, he had to bring substantial benefits, which would counterbalance significant risk of being eaten or left without food.

Based on available data, we can conclude that the dream - is not a luxury but an essential for the physical and mental health process. But scientists are just beginning to open his other complex and diverse functions.

That at this time it occurs in the brain

The brain does not turn off, are alternating two phases of sleep. Each with different characteristics: the slow (deep) and REM sleep.

Deep is about 80% of total sleep time. This phase is characterized by slow brain waves, muscle relaxation, deep breathing calm.

Also during slow wave sleep consolidating memories: recent developments are translated into long-term storage. But not all in a row - less important memories are cleaned in the past day. Connections between neurons (synapses) are reducedHomer1a drives homeostatic scaling-down of excitatory synapses during sleep in size, which is why loose connections "cut" and the impressions are forgotten.

The remaining 20% ​​of REM or rapid eye movement phase (REM). During it we dream. They can last from a few seconds to an hour. In the course of the night they become longer, but almost immediately forgotten.

In the REM phase brain is very active, paralyzed muscles, increased heart rate, breathing becomes uneven. It is believed that dreams are associated with learning and memory, Because after the new experiences we usually see more dreams. Reduction in the REM sleep time is associatedSleep architecture and the risk of incident dementia in the community with the risk of dementia.

How to sleep

It is often said about eight hours, but the optimal amount of sleep varies for different people and different periods of life. Researchers from the US National Sleep Foundation analyzed 320 scientific articles and made detailed recommendationsNational Sleep Foundation Recommends New Sleep Times.

Thus, in their opinion, the ideal amount of sleep for adults - 7-9 hours for adolescents - 8-10 hours. Young children need to sleep longer - 10-13 hours, and babies - up to 17 hours.

Adult can for some time sleep less and feel normal, if he has a good quality of sleep. But when this process takes less than seven hours, appearSleep Duration and All-Cause Mortality adverse health consequences. The same thing happens when too much sleep, although such cases is still very little.

As sleep is associated with circadian rhythms

In the 1930s, the American neuroscientist Nathaniel Kleitman (Nathaniel Kleitman) spent 32 days in a cave at a depth of 42 meters. The aim of the experiment was to study the internal clock of the person. He lived in complete isolation, trying to extend the hours to 28 hours.

And he did not succeed in spite of the strict daily diet and sleep. He still felt cheerful when his 'day' approximately coincides with the light. his body temperature also fluctuated within the 24-hour cycle. With the same faced by many working in shifts, especially with irregular schedule.

Why do we cling to the 24-hour cycle

Over millions of years of evolution, our life cycle synchronized with the change of day and night, which is caused by the rotation of the planet. circadian rhythms formed in virtually all living organisms.

And they are so ingrained in us that work even without external signals. For example, standing in a dark cabinet at a stable temperature plants folded and unfolded leaves like feel sunlight not receiving it.

In 1970, scientists have found an important part of the internal clock. During experiments with fruit flies they had identified a gene period, the activity of which is cyclical changes within 24 hours.

And scientists, two of whom subsequently won the Nobel PrizeNobel Prize in Physiology or Medicine was awarded for the study of circadian rhythms in Physiology or Medicine, was able to find out how this gene. It triggers the production of specific protein (PER), which accumulates in the cells of night and day destroyed. The level of this protein in the cell, and is used as an indicator of the time of day.

How it manifests itself

The man found a gene that is expressed in areas of the brain called the suprachiasmatic nucleus (SCN). It serves as a conduit between the retina and the pineal gland in the brain, which produces the sleep hormone melatonin. Therefore, when it gets dark, we feel sleepy.

SCN - is a main clock of the body, but there are still so-called clock genes. They are active in almost all types of cells and control the activities of approximately half of our genes.

The activity of some cells (blood, liver, kidney, lung) varies depending on the 24-hour cycle, even when the cells are in a beaker. And almost all processes in the body - from the secretion of hormones to prepare the digestive enzymes and pressure changes to temperature - heavily influenced by the fact what time of day they are usually needed.

Better to sleep earlier

Poor sleep is often associated with the modern sedentary lifestyle, availability of electricity and the use of electronic devices. However, the sleep study among the nations, is now occupied by hunter-gatherers, refutes this.

Researchers Hadza people living in northern Tanzania, foundHadza sleep biology: Evidence for flexible sleep-wake patterns in hunter-gatherersThat where people often wake up at night, and sleep modes of the individual are very different. Thus, over 220 hours of observation was recorded just 18 minutes, when all the 33 tribe members were sleeping at the same time.

As a result, scientists have concluded that restless sleep It may be an ancient survival mechanisms developed to protect against the dangers of the night. The main difference is that members of this tribe is not worried about the sleep problems.

What happens if you do not get enough sleep

In the most severe cases, lack of sleep can lead to death. For example, a rat, which is not allowed to sleep die within two to three weeks.

Naturally, such an experiment was not repeated in humans, but even one or two days without sleep can cause a healthy person hallucinations and physical distress.

After one night of poor sleep are reduced cognitive abilities, affects concentration and memory. As a result, we are inclined to impulsive decisions and momentary pleasures. And according to one studyLack of sleep and unethical conduct, Lack of sleep also increases the likelihood of lies and betrayals.

How lack of sleep affects the physical health

Regular lack of sleep has a cumulative effect. It is associated with obesity, diabetes, heart disease and dementia. People who constantly work the night shift, 29% more likely to developMeta-analysis on shift work and risks of specific obesity types obesity than those who work in shifts. Moreover, the work at night 41% increaseShift work linked to increased risk of heart attack and stroke risk of heart attack and stroke.

Of course, in this case, it is difficult to separate the effect of sleep deprivation on other factors, such as stress and social isolation. Nevertheless, there is increasing evidence of a direct effect of lack of sleep on health. Already revealed that he is workingAcute sleep loss results in tissue-specific alterations in genome-wide DNA methylation state and metabolic fuel utilization in humans the metabolism and the balance between fat and muscle mass.

It has long been known that insomnia can be a symptom of dementia. Some scientists also believe that poor sleep - one of the factors contributing to the development Alzheimer's disease.

During sleep, the brain gets rid of the protein beta-amyloid. And if you sleep enough, they accumulate and eventually lead to neurodegenerative changes in the brain.

Sleep if all the other animals

The answer depends on what is considered a dream. Most scientists understood as:

• immobility;
• significantly lower response than during wakefulness.

On the basis of these criteria, researchers have tried to identify the types of Sleepless, but hard evidence yet.

Contender for the title at one time was a bullfrog. In 1967, scientists conducted an experiment and found that these frogs are equally responsive to an electric shock during the day and at night. But these results are questioned.

There are animals who need little sleep. For example, adult giraffes in the amount of sleepBehavioural sleep in the giraffe (Giraffa camelopardalis) in a zoological garden about half an hour a day for a few minutes for the "approach". And some animals can sleep with only one half of the brain and thus remain active. Such one-hemisphere sleep, for example, occursUnihemispheric sleep and asymmetrical sleep: behavioral, neurophysiological, and functional perspectives dolphins, seals, manatees and some birds, and possibly sharks.