Old adage 'sleep on it' is true -- but only if it's a really difficult problem, study shows

A new study from Lancaster University has found that sleeping on a problem really can help people to find a solution.

The study, published online this week in the journal Memory & Cognition, tested whether sleep or time spent awake worked best in helping people find the solutions to a range of problem solving tasks.

Participants in the study -- 27 men and 34 women -- were asked to attempt easy and difficult verbal insight problems and, following a period of sleep, time spent wake, or no delay at all, the three groups of participants reattempted previously unsolved problems.

The sleep group solved a greater number of difficult problems than did the other groups, but no difference was found for easy problems.