And it’s free.Ĭo-authors of the study are Junyu Cao, who conducted research in Savage’s laboratory and is now an assistant professor at the University of Texas at Austin Alexander Herman, an assistant professor of psychiatry at the University of Minnesota, Twin Cities and Geoffrey West, a physicist who is the Shannan Distinguished Professor at the Santa Fe Institute.įunding sources included the National Science Foundation and the Eugene and Clare Thaw Charitable Trust. Adult humans have five REM cycles during a full night of sleep and can have a few dreams in each cycle.Ī good night’s sleep is excellent medicine, Poe says. The large percentage of REM sleep in babies is in stark contrast to the amount of REM sleep observed in adult mammals across an enormous range of brain sizes and body sizes. While children need more sleep, babies need much more, roughly twice as much as adults. Now when I feel tired, I don’t have any guilt about sleeping.”įor most adults, a regular seven-and-a-half hours of sleep a night is normal - and time lying awake doesn’t count, Poe says. “I would have been better off with a good night’s sleep. “I fought sleep and pulled all-nighters when I was in college, and now think that was a mistake,” Savage said. When you start to feel tired, she said, don’t fight it - go to bed. While we sleep, our brains are not resting.”Ī chronic lack of sleep likely contributes to long-term health problems such as dementia and other cognitive disorders, diabetes, and obesity, to name a few, Poe said. From jellyfish to birds to whales, everyone sleeps. “And it’s miraculous how well sleep matches the needs of our nervous system. “Sleep is as important as food,” Poe said. The significant dropoff in REM sleep at about 2-and-a-half happens just as the major change in the function of sleep occurs, Poe said. Adults older than 50 spend approximately 15% of their time asleep in REM. While newborns spend about 50% of their sleep time in REM sleep, that falls to about 25% by the age of 10 and continues to decrease with age. REM sleep decreases with the growth in brain size throughout development, the scientists found. The fraction of time spent in REM sleep before and after that point was roughly the same, whether the researchers studied rabbits, rats, pigs or humans. The data were remarkably consistent: All species experienced a dramatic decline in REM sleep when they reached the human developmental equivalent of about 2-and-half years of age. They examined data on sleep throughout development - including total sleep time, REM sleep time, brain size and body size - and built and tested a mathematical model to explain how sleep changes with brain and body size. The research team, which included scientists with expertise in neuroscience, biology, statistics and physics, conducted the most comprehensive statistical analysis of sleep to date, using data from more than 60 sleep studies involving humans and other mammals. “It’s a transition that is analogous to when water freezes to ice.” “I was shocked how huge a change this is over a short period of time, and that this switch occurs when we’re so young,” Savage said. Nearly all of this brain repair occurs during sleep, according to senior author Van Savage, a UCLA professor of ecology and evolutionary biology and of computational medicine, and his colleagues. Sleep helps repair this damage and clear the debris - essentially decluttering the brain and taking out the trash that can lead to serious illness. This transition, the researchers say, corresponds to changes in brain development.Īll animals naturally experience a certain amount of neurological damage during waking hours, and the resulting debris, including damaged genes and proteins within neurons, can build up and cause brain disease. “Don’t wake babies up during REM sleep - important work is being done in their brains as they sleep,” said senior study author Gina Poe, a UCLA professor of integrative biology and physiology who has conducted sleep research for more than 30 years.Īfter 2-and-a-half years, however, sleep’s primary purpose switches from brain building to brain maintenance and repair, a role it maintains for the rest of our lives, the scientists report Sept. During REM sleep, when vivid dreams occur, the young brain is busy building and strengthening synapses - the structures that connect neurons to one another and allow them to communicate. But why is sleep so vital to our health? A UCLA-led team of scientists has made a major advance in answering this question and has shown for the first time that a dramatic change in the purpose of sleep occurs at the age of about 2-and-a-half.īefore that age, the brain grows very rapidly. Prolonged sleep deprivation can lead to severe health problems in humans and other animals.
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