Dr. Kline points out that because college students as a group tend to get inadequate sleep, the memory capacity of the students in the study may have been below average. The nap likely was more beneficial for them than it would be for someone with a healthier sleep schedule.
“Typically students are sleep deprived because they’re up late studying and having a good time,” Dr. Kline says. “As a result, they have the ability to take a nap and catch up on some of that sleep deprivation during the middle of the day.” (In other words, the results shown in the study may not be typical.)
If you’re getting adequate sleep at night, you shouldn’t feel drowsy during the day, Dr. Kline adds. “Ideally, adults should not feel the need to take a nap,” he says. “You should try to have a sleep schedule that keeps you alert during the daytime.”
Walker agrees that people sleeping eight hours a night probably won’t feel the need for a nap. But, he says, if you do feel sleepy during the day and are able to catch some shut-eye, do it. (Just make sure you don’t push the nap back too late in the day, he warns, since napping too close to bedtime can aggravate insomnia or other sleep disorders.)
The study also provides new information on how, exactly, the brain clears storage space to make room for new memories. Walker and his colleagues monitored the brain waves of the students in the nap group while they slept, and they discovered that better performance on the 6 p.m. test correlated with a certain type of sleep: stage 2 non-REM sleep, the stage between restful deep sleep and rapid eye movement (REM) sleep, or dream sleep.
“It tells you that something very specific is going on,” Walker says. “It wasn’t just the total amount of sleep, but a very particular type of sleep that was facilitating improvements.”
The study provides more evidence that humans may not be biologically engineered to sleep one long stretch at night and stay awake all day, Walker says. Instead, our natural rhythm may be to sleep fewer hours at night and take a long afternoon nap each day, as many people continue to do in “siesta cultures” and in societies with little electricity, Walker points out.
“We’ve all had that experience of being in meetings after lunch with people who are clearly drifting off,” he says. “It’s not their fault. It’s their biology!”
