They impede both forgetting and interference

Jan 8, 2008 07:52 GMT  ·  By

Now, we know why Spaniards take their daily siesta. They want to outsmart us all! A new research led by Prof. Avi Karni and Dr. Maria Korman, of the Center for Brain and Behavior Research at the University of Haifa, and published in the journal "Nature Neuroscience", shows that a daytime nap of 90 minutes boosts the consolidation of your long-term memory.

"We still don't know the exact mechanism of the memory process that occurs during sleep, but the results of this research suggest the possibility that it is possible to speed up memory consolidation, and in the future, we may be able to do it artificially", said Karni.

Long-term memory is of two types: of "what" (a fact that took place on Monday or an article of this type read last week) and of "how to" (how to read Spanish, how to drive, play football or play the guitar).

The team put 2 groups of subjects to repeat a motor activity of bringing the thumb and a finger together at a specific sequence (a "how to" memory). The researchers focused on the subjects' performance of accomplishing the task quickly and correctly. One group napped for 90 minutes after learning the task ; the other subjects did not. The first group had an improved performance next day compared to subjects who stayed awake. But after an entire night's sleep, all subjects displayed the same skill level.

"This part of the research showed that a daytime nap speeds up performance improvement in the brain. After a night's sleep the two groups were at the same level, but the group that slept in the afternoon improved much faster than the group that stayed awake", stressed Karni.

Previous researches had shown that 6-8 hours after learning a "how to" task, this memory consolidation is sensitive to interference, induced by learning or performing a second, different task. The brain may not successfully remember the first task.

The researchers put a third group of subjects to accomplish a different thumb-to-finger movement sequence, two hours after having learned the first. The second task perturbed the memory consolidation process and the group did not display higher performance, later on the same day or next day.

But, in the case of a fourth group of subjects who took their 90-minute nap between learning the first task and the second, there were no spectacular evolutions in the evening, but next morning, they clearly displayed a much improved performance, similar to subjects lacking interference.

"This part of the study demonstrated, for the first time, that daytime sleep can shorten the time 'how to' memory becomes immune to interference and forgetting. Instead of 6-8 hours, the brain consolidated the memory during the 90 minute nap. While this study demonstrates that the process of memory consolidation is accelerated during daytime sleep, it is still not clear which mechanisms sleep accelerates in the process", said Karni.

In the end, the afternoon nap is not only for the lazybones...