You can cram all night long for the damn exam, but that's all in vain if you skip sleeping. That have been proved by a large array of researches. But this German research signaled by New Scientists comes with really astonishing information: in fact, even only 6 minutes of nap can boost your memory performances. "Ultra-short" sleep appeared to have impacted the memory processing, a challenge to current theories.

To see how short a sleep period must be to make a difference in the memory processes, the team at University of Dusseldorf tested a pool of students asked to recall groups of words, after being given an hour's break. During that break time, some of the subjects could sleep for about 6 minutes, while the others were kept asleep. To the surprise of the researchers, the napping students scored higher in the memory test. In the classic concept, the memory processing is made during the period of deep sleep, a sleep stage that takes at least 20 minutes after falling asleep.

The research team led by Dr Olaf Lahl put this boosted memory by just 6 minutes of sleep on the fact that the short nap possibly may start a cerebral process that keeps on going even if the person has got awake.

"To our knowledge, this demonstrates for the first time that an ultra-brief sleep episode provides an effective memory enhancement," wrote Lahl.

Of course, not everybody agrees with these results.

"The idea that memory could be enhanced in just six minutes is a quite unique finding and one has to be rather cautious about it. There is quite a bit of evidence that memory processing probably takes place more than six minutes into sleep." Professor Jim Horne, from the Sleep Research Center at Loughborough University, told BBC News.