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Sleep Perchance to Learn

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Science Translational Medicine  21 Nov 2012:
Vol. 4, Issue 161, pp. 161ec211
DOI: 10.1126/scitranslmed.3005327

It is well established that previously laid down memories can be strengthened during sleep and that individuals have the capacity to process a range of sensory information while they are sleeping. But we have not yet determined whether humans can acquire new information while they are sleeping. Now, Arzi et al. test this possibility in 69 healthy adults by introducing them to a range of pleasant and unpleasant odors as they slept. The authors used a unique interaction between sleep and smell to address the question of learning during sleep. They applied a technique called differential partial-reinforcement trace conditioning between tones and odors during sleep. In this method, they paired different tones with pleasant and unpleasant odors during sleep and then tested whether the tones alone, without an accompanying odor, would induce stronger sniffs by the participants if the participant associated the tone with a pleasant odor. They tested for such learned tone-induced sniffs during the same night’s sleep and during the subsequent awake phase. The authors found that partial trace conditioning between tones and odors with varying pleasantness during sleep resulted in learning of a new behavior—namely, pleasantness-dependent tone-induced sniffs—which persisted throughout the night and then when the participants were awake. These effects occurred despite application of strict exclusion criteria for arousal from sleep during the learning process.

These results demonstrate that learning does indeed occur during sleep. This study was limited by the fact that there was a relatively small number of sleeping participants who did not show arousal during the learning process. Despite this limitation, the results reveal that learning new information during natural human sleep does occur and can be implemented during the waking hours. Importantly, the authors found that this learning occurred without later awareness of the learning process, suggesting that, beyond the general health advantages associated with good sleep, the human brain is not sleeping on the job.

A. Arzi et al., Humans can learn new information during sleep. Nat. Neurosci. 15, 1460–1465 (2012). [Full Text]

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