What is the real reason people sleep?



Past research has shown that sleep has many roles, such as memory consolidation and emotional regulation, and is important not only for the brain but also for all functions of the body, including thermoregulation and the immune system. However, the question remains, “Why do we sleep? Why do we sleep? remain a mystery to this day. The BBC examines various hypotheses about the origin of sleep.

BBC – Earth – What is the real reason we sleep?

We will first examine the question, “Why do living things sleep?” The first theory to be examined is the “laziness theory” of sleep, in which animals give up consciousness for a few hours because they have finished eating, there are no natural enemies, it is not time for mating, and they have an open schedule. It is a unique theory, but basically, sleep is a disadvantageous act for creatures, even if only for a few hours a day, because a sleeping animal is far more likely to be attacked by an enemy than one that is not asleep. Therefore, the laziness theory cannot be used to answer the question, “Why do creatures sleep?” It is irrational to use the laziness theory as an answer to the question, “Why do living creatures sleep? There is also a theory that sleeping reduces energy consumption, but this is not a rational explanation either, since there is only a small difference between the state in which a human being gives up consciousness and is asleep and the state in which he or she is lying awake.

◆ Was REM sleep an evolutionary byproduct?

According to Professor Ravi Allada of Northwestern University, the most important factors that identify “sleep” are “quietness” and “lack of muscle activation. And, slower reactions compared to the conscious state and being able to recover from fatigue through sleep are also factors used for identification. Although humans can identify the sleep of other people, dogs, and cats, but not that of flies and worms, using the above requirements, it is possible to assert that even flies and nematodes are “asleep.
Today, many creatures on earth are “sleeping” with this requirement. The curious thing about sleep is that, despite its disadvantages for creatures, it has not been eliminated by natural selection, but rather has developed. Prehistoric creatures slept only in non-REM sleep, and then, for some reason, creatures that slept in REM sleep emerged.
The platypus, a “living fossil,” is a mammal that lays eggs. The platypus, which is said to have already existed during the Mesozoic Era when dinosaurs flourished, also sleeps in REM. This means that it is possible that early mammals that lived on the earth 220 million years ago were also REM sleepers. Although the dinosaurs that lived at the same time are now extinct, birds, descendants of some dinosaurs, also sleep in REM sleep, as do mammals. This suggests that REM sleep originated in mammals and birds.

So how did REM sleep originate? Some believe that the occurrence of REM sleep is an evolutionary byproduct. Monarchs, the ancestors of mammals, and caddisflies share the same amniotes. Originally, amniotes were active during the day, but as they became thermostatic, they evolved into nocturnal animals.
Nocturnal monarchs slept for a few hours during the day and were active at night to protect themselves from predators and intense sunlight, while their neural mechanisms remained the same as before evolution. In other words, amniotes originally had two time periods, one for “sitting still and keeping warm” and the other for “activity” such as feeding, social activities, and protection from predators, and the monarch brain continued to have these ancestral brain patterns. Although not translated into actual behavior by brain evolution, the brain state that monotremes inherited when they were sitting still and warming up their bodies as non-REM sleep and daytime activity as REM sleep caused their bodies to become paralyzed, which manifested as “dreams. However, this theory that REM sleep arose as an evolutionary byproduct is controversial.

◆The theory that REM sleep is caused by brain development

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 processes. It is said to regulate emotions as well as those related to memory. For example, if we try to recall our childhood, many of the memories that appear should be emotional events, such as an exciting birthday or the fear of going to school for the first time and being separated from our parents. On the other hand, while memories are emotion-based, they do not emotionally shake us in the present. This is because REM sleep remodels the memory into a form that is not attached to the emotions held in the original event. If the information is a ripe orange, REM sleep takes the bitter peel and then stores it.

One of the things that happens in the brain-memory relationship is PTSD, which is the re-experiencing of the event and the emotions held at the time of the event through flashbacks. former soldiers suffering from PTSD, when they hear a car backfiring, not only recall the battlefield in flashbacks, but also re-experience emotional reactions such as their heartbeat and sweaty palms. It has been suggested that PTSD sufferers have recurring nightmares because REM sleep does not peel the so-called “bitter orange peel.
Psychologist Rosalind Cartwright also studied the dreams of people with signs of divorce-induced “depression,” and found in a year-long study that those recovering from depression had the most prolonged miserable dreams. Conversely, those who had dreams that were not depression-like were found to suffer from depression for the longest period of time.
Based on the above study results, some researchers believe that “only mammals and birds get REM sleep” not because of the “acquisition of thermoregulation” that occurred during evolution, but because of their social and cognitive development. The reason why most animals get only 10-15% of their total sleep in REM sleep, while humans get about 25% of their sleep in REM sleep, is because of the complexity of our social interactions.

◆What is the origin of non-REM sleep?

What then are the theories about the origin of non-REM sleep, which developed prior to REM sleep and is still found in many living creatures today?
One possible origin of non-REM sleep is attributed to the “washing action of the brain. Synapses exist between neurons in the brain, and information is transmitted when neurotransmitters are released and bind to receptors. Neurotransmitters are built up in the synapses, but over time they become “congested”. This is where the process of “flushing” the neurotransmitters out becomes necessary.
In 2012, it was discovered that there is a mechanism in the brain called the “Glymphatic System,” and in 2013, it was discovered that the Glymphatic System is activated during non-REM sleep. Some researchers have hypothesized that the solute “washed” by the Glymphatic system may contain high levels of neurotransmitters. If so, “why do creatures sleep despite the many disadvantages?” If so, “to flush out neurotransmitters” would be a reasonable explanation for the mystery of “why do living creatures sleep despite their many disadvantages?
However, it is also possible that the “sleep” system developed first and the brain acquired the “flush” system as a side effect. This type of question confronts many evolutionary biologists. For example, no one can say that they are wrong about the theory that “breathing was not created to breathe in oxygen and exhale carbon dioxide, but that language was created first and breathing was created as a side effect.

In order to clarify the origin of sleep, primitive creatures such as jellyfish are currently being investigated, and single-celled creatures with two time periods, “still” and “active,” are being studied as a clue to the origin of sleep.
On the other hand, all of the above ideas are based on the idea that sleep repairs our systems that have been stressed while awake, which of course could be the wrong starting point. One could ask, “If sleep is so important, why do we have to stay awake?” And since the “origin of sleep” is still shrouded in mystery, the hypothesis that “the sleeping state existed first, and in the process of evolution, creatures have been awakened”, which sounds ridiculous at first hearing, cannot be completely denied.