A tricky problem really can be solved by “sleeping on it”, new experiments have shown. The researchers suggest our brains re-juggle data while we slumber to present us with a solution when we wake.
Anecdotal evidence has long suggested that a night’s rest can bring clarity to a complex dilemma. For example, the Russian chemist Dmitri Mendeleyev devised the periodic table following a moment of nocturnal “insight”. “He said he had a dream where all the elements fell down in the right positions,” says Ullrich Wagner at the University of Lübeck in Germany.
In the experiments conducted by Wagner and his colleagues, volunteers tackled arithmetic problems and then took an eight-hour break. Those who slept during the break were twice as likely to realise that there was a hidden rule that substantially simplified the calculations.
“We think the strongest explanation is that sleep acts on the patterns created during the training, restructuring them to give insight to the hidden rule,” says Wagner.
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He thinks the data is sifted in the hippocampus and the prefrontal cortex, areas of the brain which store and analyse memories. The team hopes next to scan the brains of people doing similar problems to spot which brain areas distinguish states of “insight” and “non-insight”
Sleepers and wakers
The arithmetic problem set for the volunteers required transforming a sequence of numbers into a second sequence by applying two simple rules. But they were only to provide the final number in the second sequence.
The hidden rule was that the final number in the second sequence was in fact always the same as the second number. Realising this would mean the volunteers could save a lot of needless calculation.
Only one of the three groups of 22 volunteers was allowed to sleep during the interlude between training and re-testing. The other two groups remained awake, one during the day and one at night, to rule out “circadian” rhythm effects.
The “sleepers” were more than twice as likely as the “wakers” to spot and exploit the short cut. “We recorded all the responses, and we could see very clearly the ‘Eureka moment’,” says Wagner.
In an accompanying experiment, the team also showed that the poor performance of the “wakers” was not simply because they were tired.
Journal reference: Nature (vol 427, p 352)
