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Olfactory Stimulation During Sleep Can Reactivate Odor-Associated Images



Research has indicated that olfactory stimuli presented during sleep might reactivate memories that are associated with this odor. The present study is the first to examine whether learned associations between odor and images can be reactivated during sleep.


Sixteen healthy, normosmic volunteers underwent a balanced learning task in which pictures of rural scenes and pictures of city scenes were associated with hydrogen sulfide (smell of rotten eggs) or phenyl ethyl alcohol (smell of roses) in the evening in a crossover design. During the subsequent night, they were stimulated with olfactory stimuli (hydrogen sulfide, phenyl ethyl alcohol, and neutral) during REM periods. Participants were awakened 1 min after the stimulation and dream reports were elicited.


The olfactory congruent stimuli significantly increased the probability of dreams about rural scenes, whereas the same effect was not found for city scenes.


As these findings support the hypothesis of reactivation during sleep, it would be very interesting to study the effect of dreams as a tool to measure reactivation of task material on sleep-dependent memory consolidation.

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Conflict of Interest

Michael Schredl declares that he has no conflict of interest.

Leonie Hoffmann declares that she has no conflict of interest.

J. Ulrich Sommer declares that he has no conflict of interest.

Boris A. Stuck declares that he has no conflict of interest.

All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2008 (5). Informed consent was obtained from all patients for being included in the study.

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Correspondence to Michael Schredl.

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Schredl, M., Hoffmann, L., Sommer, J.U. et al. Olfactory Stimulation During Sleep Can Reactivate Odor-Associated Images. Chem. Percept. 7, 140–146 (2014).

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  • Olfactory stimulation
  • Dream content
  • Sleep-dependent memory consolidation