A good night’s sleep is remarkably powerful. It restores mind and body, preparing both for the challenges that lie ahead. Without restful sleep, mood, concentration, and mental performance suffer. Sleep deprivation is a major cause of car crashes and other accidents, and it has been linked to important medical problems ranging from hypertension, obesity, and diabetes to heart disease, erectile dysfunction, and possibly even prostate cancer.
Research suggests that even a brief nap may help boost learning, memory, and creative problem solving, all while your head is on the pillow.
Setting the stage
Four reports suggest that sleep may improve cognitive function. To understand the results, though, it’s important to review the stages of sleep.
Sleep is divided into two major phases, rapid-eye-movement (REM) and non–rapid-eye-movement (NREM) sleep. Sleep begins with the NREM state. In turn, NREM sleep passes through four stages: onset (Stage 1), light sleep (Stage 2), and deep sleep (Stages 3 and 4). After about 60 to 90 minutes, REM sleep kicks in; it lasts some 20 to 30 minutes, and then NREM sleep returns to start a new sleep cycle. During the course of a normal night, a healthy adult will experience four to six consecutive sleep cycles.
NREM and REM sleep follow on each other’s heels; both are important for health, but they are vastly different. During NREM sleep, body movements continue, but eye movements are quiet or absent. Breathing slows and the heart rate and blood pressure fall. Blood flow to the brain decreases, and electroencephalograms (EEGs) show slowing of the brain’s activity.
During REM, the body is immobile, but although the lids remain closed, the eyes dart rapidly in all directions. The blood pressure, heart rate, and respiratory rate swing up and down. Blood flow to the brain increases sharply, and EEGs show spiking activity. Dreaming is most common during REM sleep, but it may also occur during the early stages of NREM sleep.
To dream, perhaps to learn
A 2010 Harvard study suggested that dreaming may reactivate and reorganize recently learned material, improving memory and boosting performance. The subjects were 99 healthy college students who agreed to avoid alcohol, caffeine, and drugs for at least 24 hours prior to the experiment. All the volunteers demonstrated normal sleep patterns before enrolling in the study.
Each of the subjects spent an hour learning how to navigate through a complex three-dimensional maze-like puzzle. After the training period, half of the students were allowed to nap for 90 minutes, while the others read or relaxed. Following a lunch break, all the volunteers tackled the virtual maze again. The only students whose performance substantially improved were the few who dreamed about the maze during their naps. Although the dreams didn’t actually depict solutions to the puzzle, the researchers believe they show how the dreaming brain can reorganize and consolidate memories, resulting in better performance on learned tasks. And all the amazing dreams occurred early in NREM sleep.
Another Harvard study tested the effects of a 45-minute daytime nap. The subjects were 33 college students; each spent 30 minutes working on the computer to master one verbal and two spatial tasks: memorizing 60 pairs of unrelated words, solving a maze puzzle, and copying an intricate figure. All the students were tested on the tasks, after which half were allowed to nap while the others rested quietly. Researchers repeated all the tests later in the afternoon. They found that NREM napping — sleeping for less than 90 minutes — further boosted performance for the students whose initial tests demonstrated good learning, but napping did not help the students who scored poorly on their first tests.
Busy people may not be able to set aside 45 minutes for a nap — but in 2008, German scientists reported that even a six-minute snooze may help improve memory. The subjects were 44 university students who were given two minutes to memorize a list of 30 words. Recall was tested an hour later, but during that hour, some of the subjects remained awake, another group napped for six minutes, and a third group took longer naps that averaged 36 minutes. The subjects who did not nap recalled an average of less than seven words; the students who napped for six minutes averaged more than eight words; and those who took longer naps averaged just over nine words. The changes may seem small, but they could come in handy if you have to tell your boss that nodding off at your desk is actually boosting your efficiency.
REM sleep and creativity
The studies from Harvard and Germany suggest that NREM napping may improve memory and learning. A 2009 report from California indicates that REM sleep may be even better, at least for creative problem solving. In the morning, the researchers gave 77 volunteers a series of creative problems and then asked them to spend the afternoon mulling over solutions before being tested at 5 p.m. One group of subjects rested quietly but stayed awake, while another was allowed to nap. All the nappers were monitored during sleep. Only those who took longer naps entered REM sleep, which occupied about 14 minutes of the 73-minute naps. NREM napping did not boost creative problem solving, but people who entered REM sleep enhanced their performance by nearly 40%, as compared with both non-nappers and NREM nappers. The improvement was specific for problems that were introduced before napping; rather than simply boosting alertness and attention, REM sleep allowed the brain to work creatively on problems posed before sleep.
Sorry to say, a nap or two won’t make you smart or assure success. But doctors know that a good night’s sleep is associated with good health, and a 2007 Greek investigation linked napping with a reduced risk of heart disease. Now four studies suggest that naps may boost intellectual performance, at least in the short term. The research shows that NREM sleep can improve memory and that REM sleep can enhance creative problem solving. It’s a two-step approach that should give every man something to sleep on.