Nature sleep

In 1953, Nathaniel Kleitman and his student Eugene Aserinsky, University of Chicago, discovered sleep marked by rapid eye movements, abbreviated as REM in English. It is REM sleep. Every terrestrial mammal has REM sleep alternating between regular sleep, called quiet sleep, in a regular cycle.

(Photo: sonnosleepcenter)

Over the past few decades, science has deepened the exploration of the nature of sleep at the nerve cell level. There are techniques for directing very small wires (about 32 microns, smaller than the smallest hair) into different brain regions. They do not cause pain, record brain activity when awake and sleep.

As expected, they show that most neurons reach or close to their peak levels when awake. But sleeping is completely different. Although the posture is immobilized or less responsive, the brain behaves completely differently during REM and non-REM sleeps.

In quiet sleep, most brain stem cells (the area of ​​the brain that connects to the spinal cord) decrease or stop the release of force, while most cortical cells and the frontal brain regions only reduce activity slightly. However, the new form of common activity is most noticeable. When consciousness, neurons often operate individually, according to the general function assignment.

In particular, a small group of cells, about 100,000 in humans, at the base of the forehead only works best in quiet sleep. These are the neurons that make sleep. The exact signal of activation of sleep-producing neurons is not fully known, but hyperthermia when awake will activate some cells. That's why we feel sleepy when taking a hot bath or at summer afternoon.

Brain activity in REM sleep is the same as when awake. Brain waves also have a low voltage due to individual cell activity. And most brain and brain stem cells work normally, signaling each other at even higher rates when awake. Brain energy consumption is as high as when awake. Strong cellular activity accompanied by eye movement causes sleep to be called REM. Some brain stem cells produce that condition and are called REM sleep cells.

Most clear dreams (which we tell when we wake up) appear during REM sleep, and dreams are often accompanied by activation of the brain's motor system, which when awake only works when we walk. Luckily, sleepwalking occurs less frequently in REM thanks to two complementary mechanisms. The brain stops secreting active cell system activators (the type of cells that regulate motor function) and releases inhibitors of these cells. But these two mechanisms do not affect the cells that control the eye muscles, so the eyes still move during REM sleep.

When people sleep, they feel the eye's activities quickly fall into a resting position. (Photo: sfn.org) REM sleep, which affects brain structures that control internal organs. Therefore, during REM sleep, the heart rate and respiration are not as regular as when awake. The body temperature is poorly regulated and tends to translate into ambient temperatures, like snakes. It is common to see male erectile dysfunction and the corresponding activity in women, although there is little sexual dream.

Function of sleep

In an international conference in 2003, most scholars agreed that sleep was still a mystery. And one way to discover mysteries is to monitor physiological and behavioral changes without sleep. More than 10 years ago, studies have shown that insomnia mice will completely die from losing too much heat (they lose weight even though they eat more). They died within 10-20 days, faster than starving but sleeping normally. In humans, a rare degenerative brain disease that causes insomnia with a family history also leads to death after a few months.

Research shows that the need for sleep increases even when the night's sleep is not significantly reduced. Sleeping while driving or working is as dangerous as drinking alcohol. And increasing sleep time with sleeping pills does not bring any clear benefits but also reduces life expectancy.

Studying sleeping habits in different species also offers an interesting suggestion. A great variety in Australia sleeps up to 18 hours, while elephants only sleep 3-4 hours daily; The closely related species do not have the same sleep time. That leads to an unusual conclusion: size is the deciding factor. Bigger animals sleep less. Elephants, giraffes, primates sleep less; Rats, cats and squirrels sleep a lot. Since then the first mystery of the nature of sleep began to reveal.

The smaller the warm-blooded animal, the higher the rate of metabolism and the body temperature (due to the body volume per unit area of ​​skin is smaller in large animals). But metabolism is the process of creating many free radicals - highly active chemicals that cause injury, even kill cells. Thus, high metabolic rate increases cell damage and its basic components. Damaged cells will be replaced by neural cells, except neuron. So the lower rate of metabolism and lower brain temperature in quiet sleep may be an opportunity to repair awakening neuron lesions.

But the theory of cell repair is not true for REM sleep, because it has an even higher metabolic rate when awake. So which group of brain cells goes against that trend? Remember the chemical signals (noradrenalin, serotonin and histamine, collectively referred to as amine) inhibiting motor function during REM sleep.

Brain cells make them strong and continuous when awake, but stop working completely during REM sleep, according to a 1973 discovery. And the second mystery of sleep reveals: Stopping release of substances This will allow their receptors to rest and regenerate gasification during REM sleep, making them work smoothly when awake.

The receptor reincarnation hypothesis has many supporting evidence. For example, deleting REM sleep will alleviate depression in mental illness. REM sleep stops releasing serotonin, so deleting it increases the release of serotonin. This reduces depression, similar to the effects of serotonin reuptake inhibitors such as Prozac or Paxil, which are often used in the psychiatric industry.

Single amine also plays a role in recombining neurons in the brain in response to new experiences. Deactivating them during REM sleep is a way to prevent unintentional changes in brain activity due to high brain activity in this sleep.

Other possibilities

What does REM sleep do? Many scientists such as Snyder or Wehr hypothesize that high activity of neurons allows animals to respond better to hazards, especially when waking up in a cold environment. We are more alert when REM awakening suggests this hypothesis is reliable.

Some scientists pursued the idea of ​​REM sleep as a role in strengthening memory, but the evidence is quite weak and conflicting. For example, people who lose REM sleep due to brain damage or drug use still have normal memory, if not more. And dolphins have impressive cognitive abilities, although there is almost no REM sleep.

Michel Jouvet, the discoverer of the brain stem, creates REM sleep 40 years ago (Photo: publihelp.fr)

The fact that learning ability is not related to REM sleep time. We only have a short REM sleep time of 90-120 minutes every night, compared to other animals. And high or low IQ is also not related to REM sleep time. But in each species and each individual, this time decreases with age.

Another function of REM sleep may be related to the level of maturity at birth of animals. In 1999, scientists saw platypus, a less evolved mammal, a record-breaking REM 8-hour champion.

At birth, this animal is blind and completely incapable of defending itself, regulating heat or seeking food, so it must stick to its mother for several weeks. In contrast, newborn dolphins were able to regulate body temperature, swim with their mothers or avoid enemies. And as adults, they hardly need REM sleep.

Michel Jouvet, who discovered the brain stem created REM sleep 40 years ago , hypothesized the long REM sleep attraction in immature animals. In the early stages of life, this high neuronal activity in sleep helps establish cellular connections that are programmed in the gene, creating what is called instinctive behavior.

In non-mature animals, REM sleep can replace external stimuli, which are crucial for neuronal development in adult animals at birth. As expected, deleting REM sleep in the experiment caused abnormal vision of the cat.

Do Kien Cuong