Two recently published studies tease out some links among sleep, learning, and memory. In the journal Child Development, researchers from UCLA’s Jane and Terry Semel Institute for Neuroscience and Human Behavior reported on the importance of sleep for academic performance. According to the LA Times, the investigators tracked the sleep patterns of 535 high school teenagers and found that “a student who gives up sleep for extra study time will have trouble the next day understanding material in class and be more likely to struggle with an assignment or test–the opposite of the student’s intent.”
The hippocampus works a bit like an old-fashioned telephone switchboard, making quick but temporary connections among the millions of nerve channels that enter it from the cortex and other regions… “We think that the hippocampus essentially links the separate features of an episode together,” says Jan Born, Ph.D., a professor of medical psychology at the University of Tübingen in Germany.
During slow-wave sleep [the deepest stage of non-REM sleep], these hippocampal links come alive again, apparently to consolidate the new memory. Experiments on rats who learn their way through mazes indicate that the same hippocampal neurons that are active during the learning of a maze are reactivated during the next period of SWS. With a similar study in humans, Pierre Maquet, D.M., Ph.D., and colleagues at the University of Liège in Belgium have shown that the degree of this hippocampal reactivation during SWS correlates with improvements in the subsequent recall of the newly learned place memories.
As noted by the LA Times article, the National Sleep Foundation recommends a little more than nine hours of sleep a night for teenagers. While that sounds wonderful, it just doesn’t seem realistic. Andrew J. Fuligni, Ph.D., the senior author of the UCLA study, suggested to the Times that “students do their best to compensate by distributing study time evenly over the week. When extra time is needed, they should consider cutting back on an activity other than sleep.”
In another study, published in Nature Neuroscience on August 26, researchers gave hope to sleep-deprived students and professionals everwhere by demonstrating that people can learn new information while sleeping. A Science Daily article notes that sleep-learning experiments are extremely difficult to perform, and that more experiments have shown the importance of sleep for memory consolidation (as mentioned above). But, researchers at the Weizmann Institute found that when they combined odor and tone cues during sleep, they influenced sniffing patterns in subjects later when they were awake.
Science Daily reports:
In the experiments, the subjects slept in a special lab while their sleep state was continuously monitored. (Waking up during the conditioning–even for a moment–disqualified the results.) As they slept, a tone was played, followed by an odor–either pleasant or unpleasant. Then another tone was played, followed by an odor at the opposite end of the pleasantness scale. Over the course of the night, the associations were partially reinforced, so that the subject was exposed to just the tones as well. The sleeping volunteers reacted to the tones alone as if the associated odor were still present–by either sniffing deeply or taking shallow breaths.
The next day, the now awake subjects again heard the tones alone–with no accompanying odor. Although they had no conscious recollection of listening to them during the night, their breathing patterns told a different story. When exposed to tones that had been paired with pleasant odors, they sniffed deeply, while the second tones–those associated with bad smells–provoked short, shallow sniffs.
While learning smells may be a long way from memorizing the Gettysburg address in your sleep, it still opens up the possibilities of sleep learning. Anat Arzi, a research student who worked on the Weizmann experiment, told Science Daily, “[W]e want to find where the limits lie–what information can be learned during sleep and what information cannot.”
--Ann L. Whitman