The German chemist Friedrich Kekule claimed to have intuited the chemical structure of the benzene ring after falling asleep in his chair and dreaming of an ouroboros (a serpent biting its own tail). He's certainly not the only person to have discovered a flash insight after waking from a good sleep. In science alone, many breakthroughs were apparently borne of a decent snooze, including Mendeleyev's creation of the Periodic Table and Loewi's experiments on the transmission of nervous signals through chemical messengers.
Most of us have tried sleeping on a difficult problem before and using an elegant experiment, Denise Cai from the University of California in San Diego has shown that this old technique really does have merit to it. She found that our brains are better at integrating disparate pieces of information after a short bout of REM (rapid eye movement) sleep - a deep, dream-rich slumber that involves a rapid fluttering of the eyes. Cai thinks that REM sleep catalyses the creative process by allowing the brain to form connections between unrelated ideas.
Cai is by no means the first person to link sleep or dreaming to creative revelations, but she is one of the few to test it directly through experiments. She asked 77 people to complete a task, where they were given a list of three words and had to find a fourth that was linked to all three. For example, 'cookie', 'heart' and 'sixteen' are all associated with 'sweet'. In each example of this 'Remote Associates Test' (RAT), the missing fourth word has a different relationship to each of the three targets.
Each volunteer was tested at 9am and 5pm on the same day and in between, they were brought into a special room at 1pm and monitored. They either rested quietly to the tune of classical music, or slept for a maximum of 90 minutes. Of the 40 who dozed off, 28 managed to get some REM sleep. Regardless of how they spent their time, all the recruits did better at the word puzzles in the second session. That's what you'd expect; the mere passage of time ought to give people a slight edge, as they mull the problems in their minds.
Some of the recruits also did a different set of tests after their morning puzzles, where they had to fill in a missing word to complete an analogy (e.g. FAST is to SLOW as HARD is to E...) Unbeknownst to them, some of the missing words were actually the answers to the earlier RAT task. This time, the recruits who got some REM sleep in the intervening time showed significant improvements in their afternoon test scores, while those who only achieved non-REM sleep or a quiet rest fared no better.
The REM naps were usually longer than the non-REM ones, but Cai found that the total length of sleep had no relation to the recruits' success at the second round of tests. It was not the quantity of sleep but its quality that made all the difference to their performance. Only REM sleep allowed them to effectively draw the link between the clues hidden in the analogy tasks and their memory of the morning RATs .
Of course, having a catnap in the day does improve a wide range of mental abilities from alertness to memory. That alone might have been behind the recruits' afternoon improvements, but Cai showed otherwise. She found that the REM-sleepers weren't any more likely than the others to remember the answers to the morning analogies, and in fact all three groups remembered about 90% of them. It was only the REM group that managed to use that information to their advantage.
Cai also found that the REM sleepers scored higher in the afternoon tests if they were given RATs that they had seen before - if they were given new sets of words, their scores were the same as the other two groups. That strongly suggests that in this case, the benefits of REM sleep lay not in boosting memory or general mental agility, but in specifically allowing the volunteers to create associations between existing ideas. Indeed, many thinkers have defined creativity as exactly that.
In 2004, Ullrich Wagner also studied the link between slumber and creativity, and showed that people are twice as likely to discover a novel solution to a mathematical problem after sleeping on it for a night. Wagner suggested that sleep might improve "cognitive flexibility" and Cai agrees.
She suggests that REM sleep (aided by falling levels of neural signalling molecules like norepinephrine and acetylcholine) helps us to incorporate new information into existing experiences. That creates a richer network of links for us to draw upon in the future and providing the fuel for flashes of insight.
Reference: Cai, D., Mednick, S., Harrison, E., Kanady, J., & Mednick, S. (2009). REM, not incubation, improves creativity by priming associative networks Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0900271106 Image of sleepy men by Bertlividet
More on sleep and creativity:
Colouring your mind - red improves attention to detail, blue boosts creativity
Portable brain activity-recorder shows that sloths aren't all that sleepy
The point of sleep, or, Do fruit flies dream of six-legged sheep?