SCIENCE DAILY
Is sleep learning possible? A new Weizmann Institute study appearing August 26 in Nature Neuroscience has found that if certain odors are presented after tones during sleep, people will start sniffing when they hear the tones alone — even when no odor is present — both during sleep and, later, when awake. In other words, people can learn new information while they sleep, and this can unconsciously modify their waking behavior.
Sleep-learning experiments are notoriously difficult to conduct. For one thing, one must be sure that the subjects are actually asleep and stay that way during the “lessons.” The most rigorous trials of verbal sleep learning have failed to show any new knowledge taking root. While more and more research has demonstrated the importance of sleep for learning and memory consolidation, none had managed to show actual learning of new information taking place in an adult brain during sleep.
Prof. Noam Sobel and research student Anat Arzi, together with Sobel’s group in the Institute’s Neurobiology Department in collaboration with researchers from Loewenstein Hospital and the Academic College of Tel Aviv — Jaffa, chose to experiment with a type of conditioning that involves exposing subjects to a tone followed by an odor, so that they soon exhibit a similar response to the tone as they would to the odor. The pairing of tones and odors presented several advantages. Neither wakes the sleeper (in fact, certain odors can promote sound sleep), yet the brain processes them and even reacts during slumber. Moreover, the sense of smell holds a unique non-verbal measure that can be observed — namely sniffing. The researchers found that, in the case of smelling, the sleeping brain acts much as it does when awake: We inhale deeply when we smell a pleasant aroma but stop our inhalation short when assaulted by a bad smell. This variation in sniffing could be recorded whether the subjects were asleep or awake. Finally, this type of conditioning, while it may appear to be quite simple, is associated with some higher brain areas — including the hippocampus, which is involved in memory formation.
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