Although sleep is characterized by a loss of consciousness accompanied by a decreased ability to respond to external stimuli, many experimental observations show that even while we sleep the mind is able to process sensory information and form new associations between sounds and smells which remain during wakefulness without the subject’s knowledge. Sleep not only allows you to consolidate memories of events experienced while awake, but also to form new associations between sensations acquired with different sense organs. This is the conclusion of a study published in the “Nature Neuroscience” journal signed by Anat Arzi department of Neurobiology, Weizmann Institute of Science in Rehovot, Israel, and colleagues from other Israeli institutions.

In the first phase of the test, different odors were administered and a clear non-verbal response was observed: the subjects inhaled more deeply when the odor was pleasant than when it was unpleasant. Subsequently, the same substances were inhaled while being uniquely associated to a particular sound for each one of them.
The following day, with the subjects awake, experimenters reproduced the same sounds but in the total absence of any odor: even in this case differences in the depth of inspiration were observed, which were higher when subjects heard the sound matched to the pleasant odor the day before. The permanence of the response during wakefulness was observed only if the conditioning had occurred during non-REM sleep.