The nature of sleep: why we sleep and how sleep deprivation affects us

2024 Author: Malcolm Clapton | [email protected]. Last modified: 2023-12-17 03:44

Science journalist The Guardian explains the importance of this biological process.

Why do we sleep

Sleep psychiatrist Allan Hobson once joked that the only known function of sleep is to cure sleepiness. Which is not entirely true, but the question of why this process is so necessary has not yet been fully resolved.

It remains unclear why sleep as an evolutionary strategy even emerged. After all, he had to bring significant benefits that would counterbalance the significant risk of being eaten or left without food.

Based on the available data, we can conclude that sleep is not a luxury, but a process necessary for physical and mental health. But scientists are just beginning to discover its other complex and varied functions.

What happens in the brain at this time

The brain does not turn off, two phases of sleep alternate sequentially. Each with its own characteristics: slow (deep) and REM sleep.

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

Also, during slow wave sleep, memories are consolidated: recent events are transferred to long-term storage. But not all of them - less important memories from the past day are cleared out. Connections between neurons (synapses) are reduced in size, because of which weak connections are "cut" and these impressions are forgotten.

The remaining 20% is REM sleep or rapid eye movement (REM). During it, we see dreams. They can last from a few seconds to an hour. They get longer as the night goes on, but are almost immediately forgotten.

In the REM phase, the brain is very active, the muscles are paralyzed, the heart rate increases, and breathing becomes uneven. It is believed that dreams are associated with learning and memory, because after new experiences we usually see more dreams. Reducing REM sleep time is associated with the risk of dementia.

How much sleep do you need

Eight hours are often talked about, 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 recommendations.

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

An adult may sleep less for a period of time and feel normal if he or she has good sleep quality. But when this process takes less than seven hours, negative health consequences appear. The same happens when there is too much sleep, although there are still very few such cases.

How sleep is related to circadian rhythms

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

And despite a strict diet and sleep schedule, he did not succeed. He still felt vigorous when his "day" roughly coincided with the light. His body temperature also fluctuated within a 24-hour cycle. Many shift workers face the same, especially with irregular schedules.

Why we are tied to the 24-hour cycle

Over millions of years of evolution, our life has been synchronized with the cycle of day and night, which is caused by the rotation of the planet. Circadian rhythms are formed in almost all living organisms.

And they are so firmly rooted in us that they work even without external signals. For example, plants standing in a dark closet at a stable temperature fold and unfold their leaves, as if they feel sunlight without even receiving it.

In the 1970s, scientists discovered an important part of this internal clock. During experiments with fruit flies, they identified the period gene, the activity of which changes cyclically within 24 hours.

And scientists, two of whom later received the Nobel Prize in Physiology or Medicine, managed to figure out how this gene works. It triggers the production of a special protein (PER) that accumulates in cells overnight and is destroyed during the day. The level of this protein in the cell is used as an indicator of the time of day.

How does it manifest

In humans, the same gene has been found that is expressed in a region of the brain called the suprachiasmatic nucleus (SCN). It serves as a conduit between the retina and the pineal gland in the brain, where the sleep hormone melatonin is produced. Therefore, when it gets dark, we feel sleepy.

SCN is the 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 activity of about half of our genes.

The activity of some cells (blood, liver, kidneys, lungs) changes with the 24-hour cycle, even when the cells are in a laboratory vessel. And almost all processes in the body - from the secretion of hormones to the preparation of digestive enzymes and changes in pressure to temperature - are strongly influenced by the time of day they are usually needed.

Did you sleep better before

Poor sleep is often associated with modern sedentary lifestyles, the availability of electricity and the use of electronic devices. However, the study of sleep among peoples now engaged in hunting and gathering refutes this.

Researchers of the Hadza people living in northern Tanzania found that people there often wake up at night, and individual sleep patterns are very different. So, for 220 hours of observation, only 18 minutes were recorded, when all 33 members of the tribe were sleeping at the same time.

As a result, scientists concluded that restless sleep may be an ancient survival mechanism developed to protect against nighttime hazards. The main difference is that members of this tribe are not worried about sleep problems.

What will happen if you do not get enough sleep

In the most severe cases, lack of sleep can be fatal. For example, rats that are not allowed to sleep at all die within two to three weeks.

Naturally, such an experiment has not been repeated in humans, but even a day or two without sleep can cause hallucinations and physical discomfort in a healthy person.

After just one night of poor sleep, cognitive abilities decline, concentration and memory suffer. As a result, we tend to impulsive decisions and momentary pleasures. And according to one study, not getting enough sleep also increases the likelihood of lying and cheating.

How sleep deprivation affects physical health

Regular sleep deprivation has a cumulative effect. It has been linked to obesity, diabetes, heart disease, and dementia. People who regularly work the night shift are 29% more likely to develop obesity than those who work shifts. In addition, working at night increases the risk of heart attack and stroke by 41%.

Of course, in this case, it is difficult to separate the effects of lack of sleep from other factors, such as stress and social isolation. However, there is growing evidence of the direct health effects of sleep deprivation. It has already been shown to affect 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 is one of the factors contributing to the development of Alzheimer's disease.

During sleep, the brain gets rid of the amyloid beta proteins. And if you don't get enough sleep, they accumulate and, over time, lead to neurodegenerative changes in the brain.

Do all other animals sleep

The answer depends on what counts as sleep. Most scientists understand by it:

• state of immobility;
• significantly lower response than when awake.

Based on these criteria, researchers have tried to identify non-dormant species, but there is no reliable evidence yet.

The contender for this title at one time was the bullfrog. In 1967, scientists conducted an experiment and it turned out that these frogs respond equally to an electric shock during the day and in the middle of the night. But these results have been questioned.

There are animals that need little sleep. For example, adult giraffes sleep about half an hour a day in total, several minutes per approach. And some animals can sleep with only one half of the brain and thus remain active. Such a one-hemispheric sleep, for example, is found in dolphins, seals, manatees and some birds, and possibly also in sharks.