A study has shown that falling asleep not only refreshes the brain, it also improves recall. Dr Olaf Lahl at the University of Dusseldorf, Germany, who led the research, believes that it is the process of nodding off - when recent events are replayed in the mind - that is so beneficial, rather than the sleep itself. He asked students to memorise a list of words and tested their ability to recall them after an hour of playing the card game solitaire.
Some of them were allowed a five-minute nap at the start of the experiment, the rest were asked to stay awake. The students who took a nap remembered significantly more words than those who were constantly awake.
''It seems much more is happening during the initialisation of sleep than we once thought,'' the Daily Mail quoted Dr Lahl as saying.
''Maybe much of sleep's functional aspects are accomplished at its very beginning,'' he added.
He said the onset of sleep triggers a period of memory processing while the deeper sleep that followed could be important for core functions such as repairing faulty connections in the brain.
The study shows it is the short period of ''thought marshalling'' rather than a period of prolonged sleep that is crucial for good recall.