Favorite odor induces negative dream emotion during rapid eye movement sleep

As connections between nightmares and various psychiatric disorders have been reported, the clinical significance of studying dream emotionality is now growing in importance. Because the olfactory bulb connects directly to the amygdala odor presentation may be a crucial tool to study dream emotions. Previous studies have demonstrated that presentation of positive/negative odors during rapid eye movement (REM) sleep affects various aspects of dreaming. Although olfactory perception can be influenced by personal experiences, the role of individual preferences in the effects of olfactory stimuli on dreaming has not yet been clarified. The purpose of the current study was to clarify the effects of odor on dreaming during REM sleep, taking individual preferences into account.

Phenyl ethyl alcohol (rose-like smell) airflow was presented as an experimental stimulus, and odorless airflow was presented as the control. Participants who like (n = 7) and dislike (n = 8) the odor of phenyl ethyl alcohol were presented air with and without the odor of phenyl ethyl alcohol, respectively, during REM sleep and then awakened to report and rate their dream contents. Thereafter, the transcribed dream reports were rated by independent raters.

Participants who liked the odor of phenyl ethyl alcohol reported more emotionally negative dreams when they were presented with phenyl ethyl alcohol airflow than that with odorless airflow. In other words, the participant's favorite odor was associated with emotionally negative dreams. These findings could be attributed to the nature of odor perception and the characteristics of brain activities during REM sleep.