What is the real reason why people sleep?

ByTomas

Sleep has many roles such as remembrance of memories and adjustment of feelings, and it is known from past research that not only the brain but also all functions of the body such as temperature regulation and immune system are important. However, "Why did people sleep? Why did they fall asleep?" Is still enigmatic. About what is "the origin of sleep"BBCWe are considering various hypotheses.

BBC - Earth - What is the real reason we sleep?
http://www.bbc.com/earth/story/20160317-what-is-the-real-reason-we-sleep

The question "Why do living things sleep?" Is considered first, "I finish my meal, there are no natural enemies, not timing of copulation, the animals will let go of conscious for several hours because the schedule is empty" It is, so to speak, the "laziness theory" of sleep. Although it is a unique theory, basically sleeping animals are much more likely to be attacked by enemies than in their state of not sleeping, so sleeping is a disadvantageous behavior even for a few hours a day, even for a living being. Therefore, it can be said that it is unreasonable to make the answer to the question "Why living things sleep"? There is also the theory that it is suppressing energy consumption by sleeping, but there are only a few differences when comparing "a state where a human releases conscious and sleeping" and "a state where it is lying as it is" The explanation is not a rational explanation.

Were REM sleep a byproduct of evolution?
According to Professor Ravi Allada of Northwestern University, the most important factor that distinguishes "sleep" is "being quiet" and "that muscles are not activated." And it is an element used for identification, such as being slow in reaction compared with a conscious state, being able to recover tiredness by sleeping, etc. Even though humans can identify sleeping of other people and dogs and cats, they can not distinguish between sleeping of flies and earthworms, but if we use the above requirements we assert that even fly and nematodes are "sleeping" It is possible.

Currently, many creatures on Earth meet this requirement and are taking "sleeping". The strange place of sleep is in the part that it is developed rather than being naturally culled, despite being disadvantageous for living things. To sleepREM sleepAlthough there are non-REM sleeps, prehistoric creatures take only non-REM sleep, and after that some creatures that take REM sleep have appeared.

It is called "living fossil"platypusIs an animal that is a mammal but lay eggs. Platypus, which is said to have already existed in the Mesozoic era where the dinosaurs flourished, also takes REM sleep. This means that there is a possibility that early mammals living on the planet 220 million years ago were also taking REM sleep. Although the dinosaurs inhabited at the same time have been extinct, birds, descendants of some dinosaurs, also take REM sleep as mammals do. From this, REM sleep is thought to originate in mammals and birds.

ByLong Road Photography (formerly Aff)

So why was REM sleep born? In response to this question, there is also the theory that the occurrence of REM sleep is a byproduct of evolution. Be an ancestor of mammalsSingle bowAnd the ancestors of reptiles are the sameAmniotic membraneis. Originally, amniotic membranes were active during the daytime, but they evolved into nocturnal animals by acquiring thermostability.

Nocturnal single bowls took a few hours of sleep during the day and protected themselves from predators and intense sunlight by acting at night, while the neural mechanism remained as it was before the evolution. In other words, the amniotic membrane originally has a time zone of "warming the body gently" and a time zone of "activity" such as feeding and social activities and protecting from predators, and a single bow The kind of brain continued to exist brain patterns inherited from these ancestors. Although the brain's evolution does not translate into actual behavior, the state of the brain when the amniotic membrane is warming the body gently warms the body gently, the non-REM sleep was taken, the daytime activity was handed down as REM sleep, the body paralyzed, That it appeared as a "dream". However, there are pros and cons for the theory that REM sleep was born as a by-product of evolution.

◆ The occurrence of REM sleep depends on the development of the brain
Contrary to the resting state of the human brain during non-REM sleep, the brain is activated during REM sleep. During REM sleep, the brain performs a variety of treatments. It is said that we are also coordinating emotions as well as memories. For example, when trying to remember things of childhood, many of the memories that appear, such as exciting birthdays, fears when going to school for the first time and becoming separated from their parents should be emotional events. On the other hand, although memory is based on emotion, it is not emotionally distracting us at present. This is because REM sleeping has been rebuilding memory in a form not attaching emotions embraced by the original event. If the information is ripe orange, REM sleep will save after taking the bitter skin.

ByMoya

One of the things that happens in the relationship between the brain and memory, re-experiences events and feelings embraced at that time through flashbackPTSDis. Former soldiers who suffer from PTSD will not only remember the state of the battlefield with flashback but also emotional reactions such as heartbeat and palm sweat when listening to the backfire of the car, Because I can not separate memory. People suffering from PTSD repeat nightmares, it is said that REM sleep is because it does not turn a so-called "bitter skin of oranges".

In addition, psychologist Rosalind Cartwright investigated the dreams seen by people with signs of "depression" caused by divorce. As a result of a year 's survey, it turned out that those who recovered from the depressed state had the miserable dream for the longest. On the contrary, those who were dreaming of a nonsense were found to suffer from depression for a long time.

Based on the research results above, "Only mammals and birds take REM sleep" is not due to the "acquisition of thermostability" that occurred in the process of evolution but also because it is developed socially and cognitively Some researchers think. Many of the animals take only 10-15% of sleep on REM sleep, while humans say that about 25% of sleep is REM sleep because complicated human social interaction .

ByLars Plougmann

◆ What is the origin of non-REM sleep?
So what is the theory about the origin of "non-REM sleep" that has developed prior to REM sleep and still found in many living things?

What is thought as the origin of non-REM sleep is attributable to "cleaning action of the brain". Between the nerve cells of the brainSynapseThere is a neurotransmitter released and information is transmitted by binding to the receptor. Neurotransmitters are built in synapses, but "traffic jam" occurs over time. Therefore, it is necessary to "wash away" the neurotransmitter.

In 2012, in the brain "Glymphatic system"It was discovered that there is a washing mechanism called" Glymphatic system "in 2013 and it turned out that the Glymphatic system became active at the time of non-REM sleep. It is said that what is contained in solutes "washed" by the Glymphatic system has not yet been analyzed, but among researchers, "There are many neurotransmitters in the solute People who make a hypothesis also ". If so, a rational explanation "To wash out neurotransmitters" is attached to the mystery "Why do living things sleep despite many disadvantages?"

However, there is the possibility that "the system of" sleep "developed earlier, and the brain got" a system to wash away "secondarily. This sort of question is that many evolutionary biologists face. For example, it is impossible for anyone to say that it is wrong to the theory that "breath was not born because of breathing oxygen and exhaling carbon dioxide, but words were first born and secondary breaths were born" It is.

In order to elucidate the origin of sleep, a single-celled creatures with two time zones of "jogging" and "acting" are now investigated about pristine living things such as jellyfish and become hints to elucidate the origin of sleep It is said that research is being conducted as.

On the other hand, all of the above ideas are based on the idea that "Sleep is restoring our system exposed to stress while I wake up," and of course there is a possibility that the starting point is wrong. "If sleep is important, why should we wake up?" It is also possible to think contrary to it, and as many "sleep origins" are still enveloped in mysteries, "sleeping Hypothesis that it seems absurd to hear that the state first exists and the living things wake up in the process of evolution "can not be completely denied.