Mysterious things that happen to your body while you sleep: John Steinbeck once noted that “it is a common experience that a problem difficult at night is resolved in the morning after the committee of sleep has worked on it.” When my head hits the pillow and I can’t seem to turn off my thoughts, I like to picture the committee gathering in a miniature boardroom in my brain. I imagine tiny committee members heatedly arguing over my dilemmas while I snooze. What a relief to leave the toughest calls up to somebody else.
Whether you’ve imagined it or not, you’ve probably benefited from such a committee’s hard work. While we doze, our brains and bodies aren’t slacking off, they’re at work, repairing us after the day’s battles and refueling us for tomorrow’s slog—in more ways than you likely realize.
There’s probably no teeny boardroom. But here’s what’s actually going on while you’re conked out:
1. You aren’t sleeping deeply most of the time.
Not all sleep was created equal: When you first drift off, you get only very light sleep, then progress deeper and deeper into dreamland. The sleep cycle starts in what’s called non–rapid eye movement or NREM stage 1 (the kind of sleep you might nab if you were the type to doze off during your college lectures; you know who you are). Then you move into a deeper NREM 2 and then to the deepest, NREM 3, also called slow-wave sleep. Finally, you land in rapid eye movement, or REM, sleep, the wild part of the ride when most of our dreams occur. The whole shebang usually takes somewhere between 90 and 120 minutes, so on a typical night you’ll cycle through four or five times, waking up for just a sec
As the night goes on, you spend less time in that deliciously deep stage 3 and more time in REM sleep, which explains why your alarm so often wakes you up in the middle of a totally bizarre dream, says Sigrid C. Veasey, MD, a neuroscientist and a professor of medicine at the University of Pennsylvania’s Center for Sleep and Circadian Neurobiology. But we don’t really know why REM periods get longer in the wee hours, says Daniel A. Barone, MD, an assistant professor of neurology at the Weill Cornell Medical College’s Center for Sleep Medicine. One theory, he says, is that REM sleep may somehow prepare you to get your butt out of bed.
2. Your brain cleans house.
Our brains are “on” throughout the night, especially in that dream-heavy REM sleep, Barone says, when they’re actually almost as active as they are when we’re wide awake.
Among other things, they may be taking out the trash. That’s one of the more exciting new ideas about the purpose of sleep: A 2013 study in mice found that waste removal systems in the brain are more active during sleep. Perhaps, the researchers theorized, we sleep to allow time to clear away toxic byproducts that would otherwise pile up and cause problems, like the trademark plaques of Alzheimer’s disease, Veasey says.
Your brain’s also busy cementing new memories while you sleep. “We think the brain is processing the information we gained throughout the day and filtering out the information we don’t need, which may be one of the reasons we dream,” Barone says. The theory goes that maybe connections between brain cells are strengthened or weakened during sleep, depending on how much we used them during the day, he says. The important stuff gets reinforced while the factoids we just don’t need get trashed.