Advice to “sleep on it" could be well founded, scientists say. After a good night's sleep a problem that seemed insurmountable the night before can often appear more manageable, although the evidence until now has been anecdotal. But researchers at the University of Luebek in Germany have designed an experiment that shows a good night's sleep can improve insight and problem-solving. "If you have some newly acquired memories in your brain, sleep acts on those memories, restructures them, so that after sleep the insight into a problem which you could not solve before increases," said Dr Jan Born, neuroscientist, at the university. To test the theory, they taught volunteers two simple rules to help them convert a string of numbers into a new order. There was also a third, hidden rule, which could help them increase their speed in solving the problem.