Sleeping on a problem really can help solve it, say scientists who found a dreamy nap boosts creative powers.

They tested whether "incubating" a problem allowed a flash of insight, and found it did, especially when people entered a phase of sleep known as REM.

Volunteers who had entered REM or rapid eye movement sleep - when most dreams occur - were then better able to solve a new problem with lateral thinking.

Proceedings of the National Academy of Sciences has published the US work.

In the morning of the test day, 77 volunteers were given a series of creative problems to solve and were told to mull over the problem until the afternoon either by resting but staying awake or by taking a nap monitored by the scientists.

Compared with quiet rest and non-REM sleep, REM sleep increased the chances of success on the problem-solving task.

The study at the University of California San Diego showed that the volunteers who entered REM during sleep improved their creative problem solving ability by almost 40%.

The findings suggest it is not merely sleep itself, or the passage of time, that is important for the problem solving, but the quality of sleep.

Lead researcher Professor Sara Mednick said: "We found that, for creative problems you've already been working on, the passage of time is enough to find solutions.

"However for new problems, only REM sleep enhances creativity."

The researchers believe REM sleep allows the brain to form new nerve connections without the interference of other thought pathways that occur when we are awake or in non-dream-state sleep.

"We propose that REM sleep is important for assimilating new information into past experience to create a richer network of associations for future use," they told PNAS.

Dr Malcolm von Schantz of the Surrey Sleep Research Centre at the University of Surrey said: "Whatever the importance of the dreams themselves are, this paper confirms the importance of REM sleep, the sleep stage when most of our dreaming takes place."

他们测试"孵化"一个问题能否使灵光乍现，结果表示是能够的，特别是当我们进入一个称为REM的睡眠阶段。

参与实验的志愿者进入较多梦的REM阶段，或快速眼动期（rapid eye movement sleep）,都较能以水平思考解决新的问题。

《国家科学研究院学报》（Proceedings of the National Academy of Sciences/PNAS）刊登美国这项研究。

在测试当天的早上，77名志愿者给派发一连串创意问题，并需要仔细思考问题直至下午，然后选择保持清醒地休息，或是小睡，由科学家观察情况。

与静静地休息及没快速眼动睡眠相比，有快速眼动期睡眠的人成功地解决问题的机会增加了。

加州大学圣地亚哥分校进行的这项研究显示，志愿者睡觉时进入快速眼动期，解决问题的创意能力提升近四成。

结果表示解决问题最重要的关键，不单是睡眠本身，或者睡眠时段，而是睡眠的质素。

首席研究员梅德里克（Sara Mednick）教授说：「我们发现，对于思考中的创意问题，睡眠时段已能够找出解决方法。」

「对于解决新的问题，只有快速眼动期的睡眠，才可以提升创意能力。」

研究员相信在快速眼动期睡眠期，大脑能不受其它思绪干扰，形成新的神经网络，那是在清醒或无梦状态睡眠时不能做到的。

「新信息吸收后并融入过去经验中，形成一个可将来使用的丰富联想网络，在这方面，我们认为快速眼动期扮演重要角色。」他们向《国家科学研究院学报》说。

Surrey大学Surrey睡眠研究中心的Malcolm von Schantz博士说：「无论梦境本身有何重要，这份研究证实了快速眼动期睡眠的重要，这是睡眠中大多梦境出现的时候。」