A new study advises a good night's sleep to all those trying to remember a new skill - it's great for boosting memory.
Scientists carried out an experiment in which sleeping volunteers were played sounds associated with a memorised task.
When they awoke, they performed better in the tests, showing their memories had been reinforced.
The results add to growing evidence that sleep is important to memory processing.
Prior to their naps, the 12 study participants were taught to associate 50 images with random locations on a computer screen. Each image, for instance a shattering wine glass, was paired with a corresponding sound played over a loudspeaker.
After a number of repeated trials the volunteers became skilled at dragging the images to their assigned places. Next, participants were allowed to dose off in a quiet darkened room, and sounds corresponding to 25 of the images were played without them waking up.
Later the volunteers repeated the matching images to locations test. They were found to be more accurate when placing images whose cue sounds had been played during sleep.
"While asleep, people might process anything that happened during the day - what they ate for breakfast, television shows they watched, anything. But we decided which memories our volunteers would activate, guiding them to rehearse some of the locations they had learned an hour earlier," Professor Ken Paller, from the Weinberg College of Arts and Sciences at Northwestern University in Chicago, said.
The sounds were played during deep sleep rather than REM (Rapid Eye Movement) sleep, the most studied phase of sleep when most dreaming occurs.
"We are beginning to see that deep sleep actually is a key time for memory processing," said Paller.
The research raises questions such as whether it may be possible to improve learning by playing recorded information during sleep, or help people forget unwanted memories.
The study has been published in the journal Science.