Haifa researchers: Daytime naps help long-term memory

A 90-minute nap during the day is enough to quicken the storage of long-term memory.

By JUDY SIEGEL-ITZKOVICH
sleep 224.88 (photo credit: ariel jerozolimski)
sleep 224.88
(photo credit: ariel jerozolimski)
If you "sleep on it" by taking a daytime siesta, you may find that the nap speeds up the consolidation of your long-term memory, according to new research conducted at the University of Haifa's Center for Brain and Behavior Research. A 90-minute nap during the day is enough to quicken the storage of long-term memory, said Prof. Avi Karni and Dr. Maria Korman, who have just published their research in the prestigious journal Nature Neuroscience. "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 doesn't disappear for many years or perhaps at all. It is divided into two types: memories of "what" (for example, what happened yesterday or what one remembers from an article you read yesterday) and memories of "how to" (for example: how to read Hebrew, drive, play basketball or play the piano). In this new research, which was conducted in cooperation with the Sheba Medical Center's sleep lab and psychology researchers at the University of Montreal, it was revealed that a daytime nap changes the course of memory consolidation in the brain. Two groups of participants practiced a repeated motor activity that consisted of bringing the thumb and a finger together in a specific sequence. The research examined the "how to" aspect of memory in the participants' ability to perform the task quickly and in the correct sequence. One of the groups was allowed to nap for 90 minutes after learning the task, while the other group stayed awake. The group that slept in the afternoon showed a distinct improvement in their task performance by that evening, as opposed to the awake group, which did not show any improvement. Following a whole night's sleep, both groups exhibited 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," Karni said. A second experiment showed that another aspect of memory consolidation is also accelerated by sleep. It was previously shown that during the six to eight hours after completing an effective practice session, the neural process of "how to" memory consolidation is susceptible to interference, such that if, for example, one learns or performs a second, different task, one's brain will not be able successfully to remember the first trained task. A third group of participants in the Haifa study learned a different thumb-to-finger movement sequence two hours after practicing the first task. As the second task was introduced at the beginning of the six-to-eight-hour period during which the brain consolidates memories, the second task disturbed the memory consolidation process, and this group did not show any improvement in their ability to perform the task, neither in the evening of that day nor on the following morning. However, when a fourth group of participants was allowed a 90-minute nap between learning the first set of movements and the second, they did not show much improvement in the evening. The next morning, these participants showed a marked improvement of their performance, as if there had been no interference at all. "This part of the study demonstrated, for the first time, that daytime sleep can shorten the time in which "how to" memory becomes immune to interference and forgetting. Instead of six to eight hours, the brain consolidated the memory during the 90-minute nap," said Karni - who added that while this study demonstrates that memory consolidation is accelerated during daytime sleep, it is still unclear which mechanisms sleep accelerates in the process. Understanding these mechanisms, the researchers said, could enable the development of methods to accelerate memory consolidation in adults and create stable memories within a short time. Until then, if you need to memorize something quickly or if your schedule is filled with different activities that require learning "how to" do things, it is worth finding the time for an afternoon nap.