Quantitative models suggest why sleep is needed and what happens during sleep

The first quantification to explain why sleep time between species and during sleep, using data from humans and other mammals from a team of scientists at the University of California, Los Angeles (UCLA) and the Santa Fe Institute (SFI) We have developed one of the models that develops as the brain grows. Importantly, the model identifies abrupt changes in sleep parameters in humans approximately 2.4 years of age, as the primary purpose of sleep shifts from neural reorganization to repair. New study reported in Scientific progressConnects phylogeny (evolutionary relationships between species) and ontogeny (development with aging of organisms) into a unified framework.

“Looking at sleep and seeing how it changes gives us insights into something really fundamental about brain development,” said a prominent professor in Shannan Province and former chairman of SFI. Yes, a paper published by a researcher. “Don’t wake your baby during REM sleep. Important work is done in the brain during sleep,” said Gina Poe, UCLA professor of integrated biology and physiology, who has been doing sleep research for over 30 years. PhD added. “Sleep is as important as food. And how well sleep matches the needs of our nervous system is miraculous. Everyone, from jellyfish to birds to whales, sleeps. We sleep. During that time, our brains aren’t resting. “Po is a senior author of a paper published by the team,”Elucidate why we sleep: Quantitative analysis reveals a sudden transition from neurodevelopmental reorganization to early developmental repair.. “

Why do mice sleep five times longer than elephants? Why do babies sleep longer than adults? Despite its ubiquity, sleep has a mystery that has puzzled scientists for decades. However, the fact that sleep is required during development and throughout the animal kingdom suggests that it acts as a biological process necessary for survival, the authors suggest. Experts suggest many possible reasons for sleep, but the two most prominent are neural reorganizations that are essential for learning and repair.

“Two of the main hypotheses enable sleep to (i) repair and clearance needed to correct and prevent neuronal damage, and (ii) nerve reorganization needed for learning and synaptic homeostasis. It will be, “they wrote. “There is also substantial and direct evidence that sleep promotes neuroplastic reorganization associated with memory learning and integration, and regulates synaptic rescaling.”

All animals naturally experience some degree of neurological damage during wakefulness, and the resulting debris, including damaged genes and proteins in neurons, can accumulate and cause brain disease. Sleep cleans this up, effectively organizes the brain, and reorganizes and repairs the brain. The west is likened to a subway restoration done at night to avoid normal traffic disruptions.

Sleep time can be roughly classified into REM (random eye movement) and non-REM (NREM). Colloquially, REM sleep is well known as “deep sleep,” but its purpose remains unresolved. A previous study by physicist and biologist West and Van Savage, PhD, a professor at UCLA and an outside professor at SFI, examined differences in mammalian sleep time. For the newly reported study, a research team that includes scientists with expertise in neuroscience, biology, mathematics, and statistics has used data from more than 60 sleep studies on humans and other mammals. We have done the most comprehensive statistical analysis of sleep up to.

They examine sleep data throughout development (total sleep time, REM sleep time, brain size, body size, etc.), build and test mathematical models, and how sleep depends on brain and body size. I explained if it would change. The model transforms the brain into a series of simple equations that capture how the brain uses energy to process information (the information needs to be reorganized). The authors enter data from a variety of studies examining sleep time, metabolic rate, and brain size in dozens of participants, from infants to adolescents.

By determining factors such as the ratio of REM to NREM to total sleep time, especially brain size, researchers could use the model to predict the purpose of each of these types of sleep. They found that REM sleep is the main cause of reorganization / learning that governs early development, whereas NREM handles routine repairs that occur throughout life. According to Savage, almost all of this brain repair happens during sleep.

Importantly, in a person about 2.4 years old, the main purpose of sleep seems to switch from building the brain to maintaining and repairing the brain, the role it maintains for the rest of life. This transition, suggested by researchers, corresponds to changes in brain development. “I was shocked at how big this was in the short term, and this switch happens when we are very young,” Savage said. “It’s a similar transition when water freezes on ice.”

Researchers have discovered a sudden change at this approximately 2.4-year-old transition point, where most of sleep transitions from REM to NREM, a phase shift from sleep to reorganization and sleep to repair. “Our findings show a sudden transition between the ages of two and three in humans,” they pointed out. “Specifically, our results show that the difference in sleep between whole phylogeny and late ontogeny (2-3 years in humans) is primarily due to sleep function for repair or clearance. It indicates that it is caused by changes in sleep during early ontogeny (2-3 years ago), mainly supporting neural reorganization and learning … “

This transition point was not previously identified and can have a significant impact on development. Savage also commented: What are the consequences of the ability to learn a language and adapt the brain to different situations? “

Scientists have found that REM sleep decreases with increasing brain size during development. Newborns spend about 50% of their sleep time in REM sleep, but by the age of 10, it drops to about 25% and continues to decline with age. Adults over the age of 50 spend about 15% of their sleep time on REM. Poe said that a significant 2.5-fold reduction in REM sleep occurs in the same way that major changes in sleep function occur.

Therefore, children need more sleep than adults, while babies need about twice as much sleep as adults. The large proportion of REM sleep in babies is in stark contrast to the amount of REM sleep observed in adult mammals over a very wide range of brain and body sizes. An adult human has five REM cycles during one night’s sleep and can have several dreams in each cycle.

“Infants spend more time in REM sleep than older children and adults,” the authors say. “This finding suggests that REM sleep is probably important for the baby’s early growth, and especially for the regulation of synaptic weight throughout the nervous system … Therefore, major changes in percent REM sleep throughout development , An important indicator of sleep function, especially REM sleep, which is very different from adults during development. “

In fact, the team’s data was very consistent across the different species they saw. All species experienced a dramatic decrease in REM sleep when they reached human development, equivalent to about 2.5 years of age. Whether researchers studied rabbits, rats, pigs, or humans, the percentage of time spent in REM sleep before and after that point was about the same. “Our analysis shows that neuroplastic rearrangements occur primarily in REM sleep, but not in NREM,” the team concluded. “This developmental transition suggests a complex interaction between developmental and evolutionary constraints on sleep.”

Chronic sleep deprivation is likely to cause long-term health problems such as dementia and other cognitive deficits, diabetes and obesity, to name a few, Po said. When you start feeling tired, she said, sleep instead of fighting it. “I spent all night fighting sleep when I was in college, and I think that was a mistake now,” Savage commented. “Good night. Now when I feel tired, I don’t feel guilty about sleep.” As Poe said, good night sleep is a good medicine. And it’s free.

For most adults, seven and a half hours of sleep per night is usually normal. The time of awakening is not important, Po said. “I would like to know if our framework can be extended to other mammals.”