The Science of “Sleeping on It”


Experts say if you want to harness sleep’s problem-solving powers to the fullest, think about your dilemma just before bed

Markham Heid
Illustration: Kieran Blakey

TThomas Edison appreciated a good midday snooze, and the great inventor’s quirky napping routine has become legend. By most accounts, Edison liked to settle into a comfortable chair with a ball bearing in each hand, and metal pie pans at his feet. After dozing for a while, Edison’s hands would relax and the ball bearings would clatter into the pans, waking him up.

All this was not without purpose. Upon waking, Edison would immediately write down whatever thoughts came to him. His belief was that many of his most inspired ideas came to him after a bit of sleep, and his napping program was designed to harness more of this slumber-induced creative energy. A new study in the journal Psychological Science suggests Edison was onto something.

For the study, researchers at Northwestern University presented people with a series of carefully designed, sneakily tricky puzzles. The participants had two minutes to try to solve each puzzle. During those two minutes, a unique sound clip would play on a loop in the background. (New puzzle, new sound clip.)


After this first stage of the experiment, which always took place in the early evening, the people went home with some specialized equipment. The equipment monitored their sleep and, as they slept, played back some of the same sound clips they’d heard while attempting to complete the puzzles in the lab. The next morning, the people returned to the lab and got another crack at the puzzles they’d been unable to solve the night before. Their solve-rate improved across the board, but they were especially adept at solving the puzzles that corresponded with sound clips they’d heard while sleeping. They figured out the answers to 32% of the sleep-cued puzzles, compared to 21% of the un-cued puzzles.

“There was this idea that during sleep the brain is resting, but now we know there’s a lot of important work being done,” says Mark Beeman, a professor of psychology at Northwestern. During sleep, the brain sorts, consolidates, and stores new information. It also “rehearses” recent memories, he says. This rehearsal seems to help the brain identify meaningful patterns while discarding unhelpful “background noise” — all of which could aid in problem-solving, he explains. Playing sound clips cued to certain puzzles appeared to facilitate this form of helpful rehearsal.

“This research adds to a growing literature suggesting that sleep can reorganize information to facilitate problem-solving,” says Kristin Sanders, first author of the study and a doctoral student at Northwestern. “It also suggests that replay of the problem memory during sleep is critical for this reorganization.”

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