Their study illuminates the complex process by which we store and retrieve acquired information -- learning, in short, the journal Nature Neuroscience reports.

Fresh memories, stored temporarily in a region of the brain called the hippocampus, do not gel immediately, earlier research showed.

It was also known that reactivation of those memories soon after learning plays a crucial role in their transfer to more permanent storage in the brain's 'hard drive,' the neocortex, according to the Daily Mail.

During wakefulness, however, this period of reactivation renders the memories more fragile. Learning a second poem at this juncture, for example, will likely make it harder to commit the first one to deep memory.

Susanne Diekelmann of the University of Lubeck, Germany, who conducted the study said: "The positive impact of short periods of sleep on memory consolidation could have implications for memory-intensive activities such as language training."

Twenty-four volunteers were asked to memorise 15 pairs of cards showing pictures of animals and everyday objects. While performing the exercise, they were exposed to a slightly unpleasant odour.

Forty minutes later, half the subjects who had stayed awake were asked to learn a second, slightly different pattern of cards.Just before starting, they were again made to smell the same odour, designed to trigger their memory of the first exercise.

Both groups were then tested on the original task. The sleep group performed significantly better, retaining on an average 85 percent of the patterns, compared to 60 percent for those who remained awake.