According to foreign media reports, about one-third of human life is sleeping. Scientists have been discussing why sleep takes up so much of our time. At present, the latest research shows that there are differences in sleep conditions among people at different ages and stages. < / P > < p > there are two main theories to explain why we mainly focus on mental activities when we sleep: one is that the brain uses sleep to reorganize the connections between cells and build neural networks that support our memory and learning abilities; the other is that the brain needs time to clean up the accumulated metabolic waste of the day. Neuroscientists have been debating which of these explanations is the main reason why humans need sleep, but new research shows that for infants and adults, the main reasons for sleep vary with age. In the study, published in the September 18 issue of the journal progress of science, researchers used mathematical models to show that infants spend most of their sleep in “deep sleep,” also known as random eye movement sleep (REM). At the same time, our brain cells rapidly establish new connections and expand, and then as toddlers approach the age of two and a half, their REM sleep time decreases rapidly, as their brains switch to “maintenance mode,” most of which is spent cleaning up and repairing brain waste. Van savage, a professor of ecology, evolutionary biology and computational medicine at the Santa Fe Institute at the University of California, Los Angeles, who wrote the study, said it was absolutely shocking that this brain pattern was switching so quickly. < / P > < p > at the same time, the researchers collected data on other mammals, including rabbits, mice and guinea pigs, and found that their sleep may undergo similar changes. However, it is too early to judge whether these patterns are consistent in many species. “I don’t think it’s actually as obvious as this, but it’s more stable, or at different ages, and the rate of brain development varies from person to person,” said Lyra taruch, a neuroscientist at the University Hospital of pediatric and adolescent psychiatry and psychotherapy at the University of Bern, Switzerland It is often “sparse.” According to a research report published in the proceedings of the National Academy of Sciences in 2007, savage and theoretical physicist Jeffrey West found that animal brain volume and brain metabolic rate can accurately predict the sleeping time of animals, which is more accurate than the prediction based on the overall size of animals. In general, large animals with larger brains and lower brain metabolic rates sleep less than small animals with opposite characteristics. For example, mice sleep longer than elephants, and newborn babies sleep longer than adults. However, sleep time decreases with brain size, and researchers want to know how quickly this change occurs in different animals, and whether the change is related to sleep function over time. < / P > < p > to begin answering these questions, the researchers collected existing data on human sleep time, collected hundreds of data points from newborns to 15 years old children, and also collected data on brain volume and metabolic rate, brain cell contact density, body size and metabolic rate, rapid eye movement sleep time ratio at different ages, and more than 60 data points These data points are obtained in the study. < p > < p > infants sleep twice as much as adults, and they tend to sleep in REM state, but for a long time, it has not been clear what role this state plays. < / P > < p > the authors of the research report established a mathematical model to track and analyze all these data points over time and observe the pattern changes of these data points. Infant brain metabolic rate is high because brain cells establish many new connections, which are related to the infant’s more rapid eye movement sleep state. As a result, they concluded that longer periods of rapid eye movement in infancy contribute to rapid brain remodeling, as new brain networks form and babies learn new skills. “This association doesn’t change very quickly,” savage said. “As babies reach the age of 2-3, their REM time will gradually decrease.” < p > < p > at the same time, the cell metabolic rate of cerebral cortex (the surface of cerebral fold) has also changed. In infancy, the metabolic rate is directly proportional to the number of existing connections between brain cells and the energy required by brain neural network to establish new connections. As the rate of brain remodeling slows down, the corresponding metabolic rate will also slow down. In the first few years of human life, the brain is making a lot of new connections, and it’s developing very fast, which is why we’re seeing a rapid learning of human skills, taruch said. Developmental psychologists call this a “critical period” of neural plasticity – the ability to make new connections between brain cells. After that critical period, neural plasticity did not disappear, but as predicted by the new mathematical model, the construction speed of new connections slowed down significantly, and the ratio of non REM sleep to rapid eye movement sleep was also increasing, which supported the view that non rapid eye movement was more important than neural plasticity in brain maintenance. Looking forward to the future, researchers plan to apply the sleep mathematical model to other animals to see if a similar transition from reconstruction to repair occurs in the early stages of animal development, savage said. “We know that human brain development is unusual after birth, so we can imagine that the human phase transition described here may have occurred earlier than other species, or even before birth,” said Cao Junyu, associate professor of information, risk and operations management at the University of Texas at Austin. < / P > < p > in terms of human sleep, taruhe pointed out that during REM sleep and non REM sleep, brain wave activity patterns are different. Considering the change of REM time, future research may reveal whether specific brain wave activity shapes the brain with age. Theoretically, disruption of these patterns may lead to developmental disorders in infants and early childhood, but this is only a hypothesis. Global Tech