A nap during the day doesn't just beat tiredness, but actually improves the brain's ability to absorb new information, claim US scientists.
Volunteers who slept for 90 minutes during the day did better at cognitive tests than those who were kept awake. The results were presented at a conference in California.
A UK-based expert said it was hard to separate the pure "memory boosting" effects of sleep from those of simply being less tired. The wealth of study into the science of sleep in recent years has so far failed to come up with conclusive evidence as to the value of a quick "siesta" during the day. The latest study, from the University of California at Berkeley, suggests that the brain may need sleep to process short-term memories, creating "space" for new facts to be learned.
In their experiment, 39 healthy adults were given a hard learning task in the morning - with broadly similar results, before half of them were sent for their siesta. When the tests were repeated, the nappers outperformed those who had carried on without sleep.
Checks on brain electrical activity suggested that this process might be happening in a sleep phase between deep sleep, and dreaming sleep, called stage 2 non-rapid eye movement sleep, when fact-based memories are moved from "temporary storage" in the brain's hippocampus to another area called the pre-frontal cortex.