Sleep is an integral part of every person’s life and essential to their health. Doctors believe that it is optimal for an adult to sleep seven hours a day, and that lack and excess of sleep are harmful.

However, many people (10-30% of the population) regularly face sleep disorders, including insomnia. Of equal importance is the quality of sleep, including the duration of its individual phases (slow sleep, REM sleep and so on) and their ratio.

Interestingly, the average duration of spontaneous daily sleep in mammals varies widely, from two to 20 hours per night. Assessing this parameter helps to better understand the physiological and other functions of sleep. It turns out that sleep duration does not correlate with brain size and cognitive abilities. Rather, it is determined by their ecology, lifestyle and how a particular animal eats.

Thus, the cyclical alternation of sleep and wakefulness was found to be important precisely in the context of nutrition and optimal energy utilization.

It is noteworthy that the temperature of the animal’s brain drops sharply during the transition from wakefulness to the phase of slow-wave sleep – that is, as the animal falls asleep. At the same time, the brain warms up again with the onset of the rapid eye movement phase of sleep (REM phase).

The REM (rapid eye movement) phase of sleep is indeed accompanied by rapid eyeball movements. In this phase, the brain is most active – and it is in this phase that humans dream.

As a result, it was concluded that the duration of the rapid sleep phase in warm-blooded animals is inversely proportional to the temperature of their body and brain. Thus, having a body temperature of only 31 degrees, monotremes (like platypus and echidna) spend about 7.5 hours in the REM-phase every day. They are followed at intermediate rates by marsupials and placental mammals (most members of this class, including humans). Finally, the shortest phase of REM sleep (only 0.7 hours per day) is noted in birds, which have the most “hot” blood – about 41 degrees.

It turns out that the phase of REM sleep plays a key role in the regulation of brain temperature and the rate of metabolism in this organ. It also helps the brain to move into a state of wakefulness.

The author of the study believes that during the slow phase of sleep brain temperature of animals should not fall below a certain critical value. Otherwise, they simply will not be able to wake up quickly in case of danger.

According to the scientist, his conclusions are quite applicable to human sleep. He emphasizes that the duration of the phase of REM sleep in Homo sapiens has average values, the same can be said about the temperature of his brain. All this rather denies the role of the REM phase of sleep in the outstanding cognitive and emotional capabilities of our species.

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That cognitive functioning – the ability to perform various mental activities closely related to learning and problem solving – changes with age is no secret. Neuroscientists also know that these differences between young and old people are due to changes in the brain’s connectivity – in how its regions interact with each other.

While the authors of previous studies mainly focused on how differences in neural networks affect how well people of different ages cope with cognitive tasks, the new work puts the problem, in the words of the scientists themselves, “upside down”. “We wondered: can we engage patterns of brain connectivity when people are not performing any tasks to predict their age?” – Chrysikou added.

The sample consisted of 547 people 18-88 years old for whom neuroimaging results from the Cambridge Center for Aging and Neuroscience (Cam-CAN) were available. Using their data, the researchers first analyzed whether connectivity between the central executive network and the brain’s passive mode network (unlike the former, it is active when a person is doing nothing, inactive, resting and immersed) could be a marker of age. To this end, they used multiple regression analysis (allows you to establish the dependence of one variable on two or more independent variables)

In addition, the scientists tested how the strength of the connection between the two networks is affected by the relevance detection network: it is activated when there is a discrepancy between what a person knows and can predict, and what he sees, hears or feels. It is this network that is responsible for conscious attention – when it is activated, the brain comes out of passive mode (and vice versa).

As the results have shown, by the functional connection between large-scale brain networks, which changes in the process of growing up and aging, it is indeed possible to guess the age of a person with high accuracy. And when the significance detection network was taken into account, it was even better to determine the number of years from birth.

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Sometimes it can be difficult to know if we can control a particular situation. Many factors affect this ability, including our mental state. Often high levels of stress, anxiety, and depression weaken our sense of control and lead people to believe that none of their actions matter, even if they really don’t.

For several decades, scientists have been trying to uncover the cognitive mechanisms that provide a sense of control. Now researchers from Portugal and the Netherlands have come closer to unraveling it. The cognitive mechanism they described in a paper published in the journal Nature Human Behavior has not previously been considered by scientists.

The authors designed a special experiment in a virtual reality space. It consisted of a house with several doors in each room. It was possible to move around the house in one of two scenarios. In the first, “controlled” scenario, the color of the door depended on which room it led to (for example, a yellow door always led only to the bathroom and a pink door led only to the living room). In the “unmanaged” house, the order of the rooms was fixed (any door in the kitchen could only lead to the bathroom, from the bathroom only to the living room).

As the participants moved around the virtual house, the scientists switched between the “controlled” and “uncontrolled” house scenarios without their knowledge. The test subjects walked around the house for a while, after which they had to answer a question asking which rooms were behind the two doors in front of them. If the volunteers did not feel in control, they answered that both doors led to the room they were supposed to get to according to a fixed scenario. Otherwise, they pointed to different rooms behind the doors that matched their color.

The scientists attributed the results to the fact that the participants’ brains were undergoing two parallel processes of learning the roles of “actor,” who could choose which room he or she wanted to go to based on the color of the door, and “spectator,” who got to the room determined by the sequence. As the scenarios changed over the course of the experiment, the brain constantly compared the results of the “actor” and “spectator” models to determine which one gave a more accurate prediction.

A stressor – weak electric shocks – was then added to the experiment to test its effect on the sense of control. Participants who received more shocks tended to take a “spectator” position. The higher their initial stress level was, the more they were affected by the stimulus. At the same time, people who could take action to avoid being hit were better at implementing the “actor” model of behavior.

The researchers proposed two hypotheses to explain this result. First, high levels of stress may trigger emotional processes that impair cognitive task performance. Second, under conditions of stress, the role of “spectator” seems more rational, since experience shows that the situation is uncontrollable

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