Sleep is as necessary as eating and breathing for all animals, including humans. People spend about one-third of their lives asleep, but the actual function of sleep is little understood and much debated. One reason for the conflicting ideas about sleep may be because the kind of sleep we need changes over our lifespans, according to a recent analysis.
“People have debated whether nerve cell repair or reorganization in the brain is the function of sleep. Our study recasts that question as when is the function of sleep about reorganization and when is it about repair?,” Van Savage, one of the authors of the study, told TheDoctor in an email.
The analysis, led by researchers at the University of California, Los Angeles, suggests that the reason the body needs sleep changes when children reach about two-and-a-half years of age. Before two-and-a-half, our brains are developing very rapidly, and sleep is the opportunity to consolidate brain development.
“It is miraculous how well sleep matches the needs of our nervous system.”
“Never wake babies up during REM sleep, when vivid dreams occur. Important work is being done in their brains as they sleep,” Gina Poe, another author of the study, said in a statement.
After about age two-and-a-half, the purpose of sleep shifts to repair. All animals, including humans, accumulate nerve cell damage during their waking hours. The resulting debris, from damaged genes and proteins, can build up and eventually cause brain disease. Sleep helps repair this damage and clear the debris.
Instead, the pattern they found when analyzing sleep from childhood on was abrupt and discontinuous — more like the kind of biological change that turns water into ice.
They found significant changes in REM sleep. As the brain grew during development, the time spent in REM sleep decreased. Newborns spent about 50 percent of their total sleep time in REM sleep.
“Never wake babies up during REM sleep, when vivid dreams occur. Important work is being done in their brains as they sleep.”
The amount of time spent in REM sleep fell to about 25 percent by age 10, and continued to decrease with age. For adults 50 years old or older, only about 15 percent of total sleep time was REM sleep. The decrease in REM sleep at about two-and-a-half years old happened at the same time the main function of sleep began to change.
“It is miraculous how well sleep matches the needs of our nervous system,” said Poe, a professor of integrative biology and physiology at UCLA.
The study is published in Science Advances.