Ever wondered why sleeping on a problem works? It seems that as well as strengthening our memories, sleep also helps us to extract themes and rules from the masses of information we soak up during the day.

Bob Stickgold from Harvard Medical School and his colleagues found that people were better able to recall lists of related words after a night’s sleep than after the same time spent awake during the day. They also found it easier to recollect themes that the words had in common – forgetting around 25 per cent more themes after a waking rest. “We’re not …