Science of sleep: part 1

In this post I will share information about my subject of adoration. About what I can do at any time, in any place and in any quantity. The fact that I would prefer diamonds and restaurants from the Michelin list. H- + yes, the end of this joke would have been more ridiculous if the title did not reveal the details of what I will tell about the dream. Anyway.

A dream, as necessary, and so mysterious, still puzzles scientists - and they have been researching it for decades (and people have been sleeping for thousands of years). What exactly happens in a dream? Why do we sleep? Can I stop sleeping? What happens then? Interested? Then read on, and you will find out how close we come to answering these questions.

1. Theoretical foundations: what and how is arranged in the field of sleep

Everyone has heard about the REM phase: either because of her connection to dreams, or because of her importance to a person, or simply because you liked the song " Losing My Religion ". But sleep is more: it contains three more phases with different characteristics and functions (and with different probabilities that you will be angry when you are awakened at this stage).



1st phase of sleep, N1 - the phase of drowsiness, in which you switch between waking and sleeping. Your muscles are not yet completely relaxed and you may experience a sensation of falling - a sudden contraction of muscles, a myoclonic jerk (some scientists suggested that it may flow from the brains of our primate ancestors and confuse muscle relaxation with a fall from a tree). In addition, there is a change in brain waves, synchronous electrical impulses, appearing due to the communication with each other of a huge number of neurons (see Fig. 1 for visualization of all possible brain waves). In the waking state, your brain produces many waves called beta and gamma. They twitch rather sharply and have a high frequency, and are either related to concentration (beta), or are thought to play a role in the creation of consciousness (gamma). In this first phase of sleep, your brain begins to produce slower and synchronous alpha waves instead of beta and gamma waves (they are associated with relaxation and pacification), and even slower theta waves (they are associated with deep relaxation and drowsiness) - that is, it slows down. This phase lasts from 1 to 10 minutes.


Fig. 1: a brief introduction to the waves appearing in your head

2nd phase of sleep, N2. In this phase, your consciousness has already turned off. Pulse and breathing slow down, the temperature decreases, you prepare to go into deep sleep, theta waves are still pronounced. This phase, together with the previous one, is what is called “shallow sleep”. We spend most of the night (about 45%) in this phase. From a shallow sleep, waking up is best; you will not feel overwhelmed or disoriented, but refreshed and ready for a new day .

3rd phase of sleep, N3. Here everything is serious: this is the phase of deep sleep. It is also called the phase of slow waves, because - you guessed it - brain waves slow down and become larger. Now the delta-wave ball, the slowest of all that your brain is capable of, rules. You do not react to surrounding sounds, it is difficult for you to wake up, and your muscles are completely relaxed. This phase of sleep is called regenerative, because your tissues are restored , energy is renewed , the kidneys cleanse the blood — well, you understand. If you wake up during deep sleep, you will find yourself in this state (a scientifically proven fact):



REM-phase + sleep paralysis: dreams are probably the most interesting features of sleep, mostly come at this stage, and are bright and complex. The defining property is the random and rapid movement of the eyes from side to side. The purpose of these movements is not yet completely clear (and what is completely clear in neuroscience?), Among theories - scanning those scenes that we see in a dream, as well as the formation of memory (let's talk about these sleep functions later). Your blood pressure and breathing rise almost to the level of wakefulness, the brain waves also resemble this level - even a large number of beta waves are present! Because of all these oddities, the REM phase has earned the name "paradoxical sleep." It's scary, but it's worth knowing that your muscles are completely paralyzed at this moment - the neurotransmitters GABA and glycine prevent the flow of brain signals to the muscles and protect you from reacting to sleep and possibly harming yourself. It turns out that, in fact, you just lie completely paralyzed while your eyes rush uncontrollably to and fro. Charming. Scientists believe that when the transition to the REM phase and the exit from it do not go smoothly, it can lead to sleepy paralysis - a frightening state when your consciousness has regained, but you still cannot move. In this intermediate state between wakefulness and vivid dreams, people often talk about how they see all sorts of nightmares that can usually be divided into categories such as incubi (a person feels pressure on his chest and has difficulty breathing, and can perceive it so that A certain demon sits on his chest, uninvited guests (a person feels the unwelcome presence of a certain terrible creature) and a feeling of leaving the body. This explains the many stories about paranormal phenomena and alien abductions (sorry, Agent Mulder!) About 7.6% of all people suffer from sleepy paralysis, and this proportion is quite high among students , to 28%.

During an average night, a person usually goes through several sleep cycles (each of which lasts about 90 minutes), and closer to the morning, the REM phases increase.


Overview of what is happening at night. It can be seen that at the beginning of the night the phase of the slow waves prevails, and in the second half of the sleep period the REM phase begins to predominate.

2. How does the brain go to sleep?

It is impossible to determine the exact moment of falling asleep. At one point, you are still thinking about the stupid act that you did five years ago, and at another you are already sliding towards the second phase of sleep. So what happens in the brain while falling asleep?

In the depths of your brain there is such a tiny thing as the suprachiasmatic nucleus (SCN), which controls our 24-hour sleep-wake cycle. It receives directly from the eyes information about the amount of light in the place where you are. It uses this information to reset your internal clock to match the normal day-night cycle. The internal clock accordingly regulates many functions of the body - temperature, hormone release, and what interests us now is sleep and wakefulness . It is interesting that even with the complete absence of light, our internal clock operates at approximately 24-hour rhythm . It was discovered that this is possible due to the cyclic activity of certain genes (according to what are called " clock genes "). These genes produce different levels of different “clock proteins” depending on the time of the day - and these proteins regulate daily rhythms (body temperature, melatonin production, concentration, etc.)

SCN is associated in a complex way with - get ready for the next long name - the ventrolateral nucleus of the visual mound (VLA) - the structure that remains active during sleep. It is believed that these connections activate VLA and contribute to the onset of sleep - because during the activation of VL neurons, they release inhibitory chemicals (GABA and galanin), which in turn suppress our awakening system. So, through a long chain of command, the switch turns and your waking state slowly descends to zero. VLA neurons can also be activated by a chemical called adenosine . Adenosine gradually accumulates during the day as a result of the breakdown of glycogen, which stores energy in the body, and after it has accumulated enough, it begins to increase fatigue and push you to rest. This is called homeostatic regulation, during which the brain tries to balance fatigue with rest.


Overview of the chain of command

Another chemical compound related to sleep can be found as a dietary supplement in a supermarket [in the USA / approx. transl.]: melatonin . It is produced by the pineal body , and its production, like many other substances, is regulated by circadian rhythms. When the sun goes down, the SCN gives the pineal body a command to start producing melatonin (whose presence in the body is hardly traced during the day), it enters the bloodstream and causes sleep. Recently, scientists have warned us about the dangers of using smartphones, televisions, and other light-emitting devices at bedtime, because they violate our melatonin levels. In the light of electronic devices, the concentration of the blue component is much stronger than in the natural one, and this treacherous blue light suppresses melatonin production more strongly than light of any other frequency. It confuses the sleep-wake cycle and can lead to a deterioration in the quality and quantity of sleep, as the brain becomes confused with what time of day it is. So do yourself a favor and read a book before bedtime. Or do some meditation. Or having sex. Anything without blue light.


Comparison of reduced melatonin production due to bright light (circles) and increased production when wearing glasses that block blue light (white triangles), as well as normal melatonin production in dim light (black triangles)

3. Why do we sleep, and how is sleep important?

Very good question. Unfortunately, there is no definite answer to it. As William Dement, the founder of the Stanford Sleep Research Center, said: "As far as I know, the only very, very good reason for which we need to sleep is that we become sleepy." So let's just look at what we already know (except this grain of wisdom).

Memory

The existence of a romantic relationship between sleep and memory consolidation (that is, its stabilization) was suspected by scientists for a long time, and in recent decades, if not centuries, many studies have been carried out, supporting this opinion (but none of them was completely convincing). There is a difference between two types of memory: declarative (about information based on facts, answering the question “what?”) And procedural (answering the question “how?”, For example, muscular memory of driving a bike or playing the guitar). It would be very convenient if we had a clear distinction like “sleep with slow waves is responsible for this, and the REM phase is responsible for that,” but, unfortunately, in reality everything is mixed up.

Usually, sleep helps memory work : people who sleep after they learn something usually remember new information better than those who did not sleep after learning. Learning word lists , complex finger movements, or even unraveling complex hidden patterns — all benefited from having a sleep after the learning process.

There are theories that sleep with slow waves (MWS), prevailing in the first part of the night, especially helps to consolidate the declarative memory. It is believed that the stabilization of newly acquired memories occurs through their reactivation in the hippocampus, our memory center, during sleep. By “replaying” the memories, the brain stabilizes their tracks , thereby reducing the likelihood of their loss. One study found that if you study something new, breathing in the smell of a rose, and then giving that smell to a sleeper during MWS, the activity of his hippocampus increases, and the memory the next day is fixed more strongly . So that:

1. During MWS, hippocampal reactivation is enhanced.
2. Memory improves.
3. ???
4. Profit!

The REM phase, on the other hand, is associated with procedural memory , whose consolidation does not depend on the hippocampus (rather it depends more on the repetition of commands for movement in the parts of the brain involved in muscle control — the cerebellum, basal ganglia and motor cortex). As for the exact mechanisms of consolidation of this type of memory, so far little is known, so this paragraph will be short. However, there are studies that do not agree with such a clear division (scientifically speaking, objecting to the hypothesis of the dual process ). For example, it was shown that SMW sleep can help consolidate motor (= procedural) memory, and the REM phase plays a certain role in stabilizing memories of events and facts. Apparently, not such a clear separation of duties. This suggests that both phases are important for both types of memory (this theory is called the “consistent hypothesis”): they do not compete with each other, but complement each other. It just happens that one phase (MW) can make a greater contribution to one type of memory (declarative), and vice versa.

But this, of course, does not end the story. There is - suddenly! - another theory trying to describe memory consolidation. It is called “synaptic homeostasis” and, in fact, claims that while you are awake and gaining new memories and experiences, the connections between your brain cells (synapses) are strengthened (and new ones are created), and that when you sleep, the brain trying to reduce this huge daily increase to a reasonable level, eliminating unnecessary synapses. So, we can say that we sleep to forget - and raise the signal level above the noise level, starting a new day refreshed and ready for a new training. Unnecessary connections and casual memories are removed, and important ones are enhanced through repetition. A recent study found direct visual evidence of this hypothesis: using high resolution microscopy, researchers first determined the size and shape of 6,920 synapses, and then showed that after a few hours of sleep, 80% of the synapses decreased by about 18%.


Large waking mouse synapses and shrunken synapses of a slightly sleeping mouse.

Of course, there is no right answer - the truth is somewhere in the middle, and all these theories explain only a part of what is happening. But now you will think twice before deciding to study all night before the exam; straining and throwing energy, you do not force the brain to remember information better - but it can make a few hours of sleep.

Housekeeping

Another perceived sleep function is housekeeping. While you sleep, the brain pulls the form of a cleaner and goes to clean up all the garbage that has accumulated there during the day’s thinking. In several studies in mice, researchers found a system that eliminates the waste of the brain from it during sleep. It is responsible for the cerebral analogue of the lymphatic system, a network of tiny tubules that flush out side waste with the help of cerebrospinal fluid. Scientists called it the " glymphatic system " because it works like a lymphatic system, but with the help of auxiliary cells of the brain, glia . When the mice fell asleep, this system turned on to its fullest (during wakefulness its activity is only 5% of the flow in a dream!) And the brain cells even shrank a little in size so that the place around them was easier to clean. Disposable byproducts of activity include proteins such as beta-amyloids - the villains behind Alzheimer's disease (during sleep they are washed twice as fast as they are awake!) - and other substances associated with neurodegenerative diseases. So if you suddenly want to work all night, think about all these toxins that accumulate in your brain, and instead of a night of work, sleep at least a couple of hours.

In general, although it is not yet completely clear why we spend a third of our lives in a dream, we already have pretty good guidelines.

In the second part of the article, I will reveal amazing information about dreams, about what can disrupt sleep, and give some tips about the optimal organization of sleep. Do not switch.