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Sleep and problem solving

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‘Dreaming can help you solve problems’, reported The Sun. It said that volunteers in a US study were given puzzles before and after a nap, and REM sleepers improved by up to 40%.
Brought to you by NHS Choices

This study provides information that may help scientific understanding of how sleep or rest influences creative problem-solving. However, the study has limited application to everyday life, and it is uncertain whether REM sleep helps with solving real-life or work-related problems, rather than simple word association tests.

Where did the story come from?

The research was carried out by Denise J Cai from the Department of Psychology at the University of California and colleagues from the University of California and University of Southern California. The work was funded by the National Institutes of Health. It was published in the peer-reviewed scientific journal PNAS.

What kind of scientific study was this?

In this experimental study, the researchers investigated the role of rapid eye movement (REM) sleep on creative problem solving. They claimed that previous research has suggested that sleep has a role in creative problem solving but the stage of sleep at which this occurs, and whether it is REM sleep in particular, has not been examined.

This study used an experimental sleep situation where the subjects were given varied prior exposure to a creative problem. It was designed to examine the contributions of memory and associative processing in forming a solution. The study involved 77 healthy subjects aged between 18 and 35 who were asked to rest during the week before the test.

In this study, REM sleep was directly compared with non-REM sleep (NREM) and with controls, who remained awake but rested. The subjects were compared using a test of creative problem solving called the Remote Associates Test (RAT). The RAT is a pencil and paper task in which the subject is given a set of three seemingly unrelated words and asked to produce a word that could be linked with all three of them. For example, the word “sweet” could be added to the words “cookie”, “sixteen” and “heart”.

All subjects were tested on the RAT twice in the same day. One version of the RAT was completed in the morning and the results were compared to those of another test in the afternoon. At 1pm, the subjects were randomly assigned to either sleeping (which was defined as either 90 minutes sleeping or up to two hours in bed; therefore this may have included REM or NREM sleep depending on how deeply the subjects fell asleep) or a rest situation, where the subjects listened to relaxing music for 90 minutes. Brain activity was monitored during both rest and sleep situations. They were then given the RAT again at 4.30pm.

The researchers gave different subjects different versions of the RAT, which were designed to give the subjects the following prior exposures for their afternoon tests:

  • Repeated exposure to the same creative problem in the morning and afternoon, , i.e. identical questions in the morning and the afternoon.
  • ‘Priming’ the subjects in the morning test for what would be included in their afternoon test, i.e. answers to certain questions in the morning test would also be the answer to different questions in the afternoon test.
  • No prior exposure, where the subjects were given unrelated tests in the morning and afternoon.

The researchers expected that those given the same questions twice a day would be better at problem solving in the afternoon due to repeat exposure, but that REM sleep would be needed so that information from primed questions could be used to give a creative solution to associated but separate questions in the afternoon. They expected that in the test where the subjects were given no prior exposure and a completely different set of questions in the morning and afternoon, sleep would be of no benefit in solving a creative problem.

What were the results of the study?

As expected, giving the subjects the same problems in the afternoon as in the morning resulted in significantly increased performance, regardless of whether they had quiet rest, REM sleep or NREM sleep in between.

With priming in the morning using separate tasks, REM sleep enhanced the subjects’ ability to find the answers to the afternoon tests; an effect which was not seen following quiet rest and non-REM sleep.

When a completely different set of RAT tests were given in the afternoon, performance was no different between those who had quietly rested, gone into REM sleep or NREM sleep.

What interpretations did the researchers draw from these results?

The researchers say their study shows that, compared with quiet rest and non-REM sleep, REM sleep enhances the integration of unrelated information allowing creative problem solving. They say this process could be facilitated by certain chemical changes in the brain and nerve cells that occur during REM sleep.

What does the NHS Knowledge Service make of this study?

This complex study has a number of limitations, the first of which is the relatively small number of subjects it included. As such, results may not be representative of those that would be seen in a larger sample. Also, it would not have been possible to randomly assign people to having REM or NREM sleep, so the results may be due to factors other than the level of sleep the subjects achieved. The researchers also carried out multiple statistical tests, which increases the likelihood that any significant results found may have occurred by chance.

Additionally, it does not appear that each subject was randomised to each of the three exposure scenarios and then to either rest or sleep intervals between each exposure (i.e. requiring six days of testing for each person). This means that there may be individual differences between subjects and how they would respond to different rest or exposure setups. This would decrease the reliability of the results if not all people tested received the same range of tests.This study could help other researchers in understanding how sleep influences creative problem-solving. However, an experimental situation such as this has limited application to everyday life and it is unknown whether the same effect of REM sleep would be seen with solving real-life or work-related problems, rather than simple word association tests.

Links to the headlines

Sleep on problem. The Sun, June 10 2009

Problems are solved by sleeping. BBC News, June 10 2009

Tests find benefit of sleeping on job. The Independent, June 10 2009

Links to the science

Cai DJ, Mednick SA, Harrison EM, Kanady JC and Mednick SC. REM, not incubation, improves creativity by priming associative networks. PNAS Published online before print June 8

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