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Deep sleep is essential for problem-solving and improving insight, German researchers say.
updated 1/21/2004 2:11:54 PM ET 2004-01-21T19:11:54

Everybody feels refreshed following a good night’s sleep. But can you wake up smarter? More artistic perhaps?

German scientists say they have demonstrated for the first time that our sleeping brains continue working on problems that baffle us during the day, and the right answer may come more easily after 8 hours of rest.

The German study is considered to be the first hard evidence supporting the common sense notion that creativity and problem solving appear to be directly linked to adequate sleep, scientists say. Other researchers who did not contribute to the experiment say it provides a valuable reminder for overtired workers and students that sleep is often the best medicine.

Sleep-deprived Americans
Previous studies have shown that 70 million Americans are sleep-deprived, contributing to increased accidents, worsening health and lower test scores. But the new German experiment takes the subject a step further to show how sleep can help to turn yesterday’s problem into today’s solution.

“A single study never settles an issue once and for all, but I would say this study does advance the field significantly,” said Dr. Carl E. Hunt, director of the National Center on Sleep Disorders Research at the National Institutes of Health.

“It’s going to have potentially important results for children for school performance and for adults for work performance,” Hunt said.

Scientists at the University of Luebeck in Germany found that volunteers taking a simple math test were three times more likely than sleep-deprived participants to figure out a hidden rule for converting the numbers into the right answer if they had eight hours of sleep. The results appear in Thursday’s issue of the journal Nature.

The study involved 106 people divided into five separate groups of equal numbers of men and women ages 18 to 32. One group slept, another stayed awake all night, and a third stayed awake all day for eight-hour periods before testing following training in the main experiment. Two other groups were used in a supplemental experiment.

The study participants performed a “number reduction task” according to two rules that allowed them to transform strings of eight digits into a new string that fit the rules. A third rule was hidden in the pattern, and researchers monitored the test subjects continuously to see when they figure out the third rule.

The group that got eight hours of sleep before tackling the problem was nearly three times more likely to figure out the rule than the group that stayed awake at night.

Jan Born, who led the study, said the results support biochemical studies of the brain that indicate memories are restructured before they are stored. Creativity also appears to be enhanced in the process, he said.

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“This restructuring might be occurring in such a way that the problem is easier to solve,” Born said.

Born said the exact process in the sleeping brain for sharpening these abilities remains unclear. The changes leading to creativity or problem-solving insight occur during “slow wave” or deep sleep that typically occurs in the first four hours of the sleep cycle, he said.

The results also may explain the memory problems associated with aging because older people typically have trouble getting enough sleep, especially the kind of deep sleep needed to process memories, Born said.

“Even gradual decreases in the total time for slow wave sleep and deep sleep is correlated to a kind of decrease in memory function, and in turn to a decrease in the ability to recognize hidden structures or the awareness of such things,” Born said.

When insight occurs
Other researchers said they have long suspected that sleep helps to consolidate memories and sharpen thoughts. But until now it had been difficult to design an experiment that would test how it improves insight.

History is dotted with incidents where artists and scientists have awakened to make their most notable contributions after long periods of frustration. For example, that’s how Russian chemist Dmitri Mendeleev established the periodic table of elements and British poet Samuel Taylor Coleridge wrote his epic “Kubla Khan.”

Born and his team “have applied a clever test that allows them to determine exactly when insight occurs,” wrote Pierre Maquet and Perrine Ruby at the University of Liege in a commentary on the research, also published in Nature.

Maquet and Ruby both say the study should be considered a warning to schools, employers and government agencies that sleep makes a huge difference in mental performance.

The results “give us good reason to fully respect our periods of sleep — especially given the current trend to recklessly curtail them,” they said.

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