In fact, he says, extensive evidence suggests that slow-wave, non-REM sleep “still seems to carry the majority of health benefits,” including regulating blood flow and blood glucose levels, and clearing Alzheimer’s-related plaque from the brain. Walker, too, believes that dreams and REM sleep have benefits - but he says it’s not the only stage of sleep that matters. (It’s worth noting that these studies only prove associations - not whether one problem actually causes or contributes to the other.) In his recent review, Naiman writes that dreaming has effects on memory and mood, and cites research linking poor-quality REM sleep to conditions like Alzheimer’s disease and depression. Other studies have suggested that REM sleep may be important for other reasons, but there’s less evidence of direct, REM-specific benefits in these areas. “When that happens, we believe that the amygdala may become less sensitive to stimuli, and less likely to overreact to something that really shouldn’t be fearful,” says Lerner. One theory, known as the REM calibration hypothesis, holds that norepinephrine builds up during the day and can be reset to normal levels during REM sleep. MORE: How Dream Therapy Can Change Your Life “Norepinephrine is associated with stress, and it affects the degree to which the amygdala - the fear center of the brain - is sensitive to stimuli,” says Itamar Lerner, co-author of the new paper and a postdoctoral sleep researcher at Rutgers University. But the part of the brain that secretes norepinephrine during wakefulness and non-REM sleep takes a break during REM sleep. Researchers aren’t certain why this happens. “The more REM, the weaker the fear-related effect,” the authors write in their paper. “It provides a nocturnal soothing balm that takes the short edges off of our emotional experiences so we feel better the next day.”Īdding to that research, the most recent study - from researchers at Rutgers University - suggests that the quality of a person’s sleep before a traumatic event can play a role in how the brain reacts to a scary situation. “I think of dreaming as overnight therapy,” Walker says. Walker and his colleagues have also found that people who view emotional images before getting a good night’s sleep are less likely to have strong reactions to the same images the next day, compared to those who didn’t sleep well. Walker’s research, for example, has demonstrated that people who achieved REM sleep during a nap were better able to judge facial expressions afterward than those who’d napped without reaching REM. Several studies in recent years have suggested that REM sleep can affect how accurately people can read emotions and process external stimuli. What are the health benefits of REM sleep? “Everything we see, every conversation we have, is chewed on and swallowed and filtered through while we dream, and either excreted or assimilated,” he says. Naiman describes the brain during REM sleep as a sort of “second gut” that digests all of the information gathered that day. Scientists are divided as to whether dreams are simply a product of random neurons firing during sleep, or if they’re something more - like a data dump that helps the brain separate important memories from non-important ones, or a way for people to prepare for challenges and play through different scenarios in their heads. (The dreams you remember when you wake up are only part of REM sleep, says Walker in reality, the brain is highly active throughout the entire phase.) But there is also decreased activity in other regions, like the one involved in rational thought - hence the reason for extremely lucid, but often nonsensical, dreams. And because longer periods of REM sleep only happen during the final hours of sleep (in the early morning, for most people), it can get cut off when you don’t spend a full seven or eight hours in bed, says psychologist Rubin Naiman, a sleep and dream specialist at the University of Arizona Center for Integrative Medicine and the author of a recent review about dreaming published in the Annals of the New York Academy of Sciences.ĭuring REM sleep, there is more activity in the visual, motor, emotional and autobiographical memory regions of the brain, says Matthew Walker, professor of psychology at the University of California, Berkeley and author of the new book Why We Sleep. REM sleep stages tend to be relatively short during the first two-thirds of the night as the body prioritizes deeper, slow-wave sleep.
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