Can We Learn While We're Asleep?

Learning things during sleep seems like a dream. To determine whether a new association between unrelated stimuli can be conditioned during sleep, researchers used nontrigeminal odors, which normally do not wake people up, as unconditioned stimuli paired with different auditory tones as the conditioned stimuli in 55 normal, medication-free participants. Sleep stages were confirmed by polysomnography. During sleep, participants heard a series of tones paired with a pleasant odor (which produces an increased volume of sniffing during wakefulness), paired with an unpleasant odor (which produces a smaller volume of sniffing), or not paired.

The odors increased delta sleep; conditioning of the tone to the pleasant smell — as demonstrated by incre…