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

Olfactory loss is associated with symptoms of depression. The present study, conducted on a large cohort of mostly dysosmic patients, aimed to investigate whether improvement in olfactory performance would correspond with a decrease in depression severity. In 171 participants (157 dysosmic), we assessed olfactory function and severity of depression before and after an average interval of 11 months, with many patients showing improvement in olfactory function. Separate analyses were conducted for (a) the whole group of patients and (b) the group of dysosmic patients using both classic and Bayesian approaches. For odor identification, Student t test demonstrated that the whole sample improved consistently, especially within the group of dysosmic patients. The dysosmic group also improved in odor threshold and overall olfactory function. Pearson correlation showed that an increase in olfactory function was associated with a decrease in depression severity, particularly in dysosmic patients. To conclude, the present results indicate that symptoms of depression change with olfactory function in general and odor identification in particular.

No abstract