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Objective: Odor presentation is a crucial tool in the experimental investigation of dreaming since odors rarely cause arousal, and are processed in the brain during sleep. Our previous study demonstrated that the presentation of a preferred odor during rapid eye movement (REM) sleep-induced negative dream emotions. However, preference and familiarity of an odor are known to be strongly related to each other in olfactory perception. Consequently, the above result might have been due to the confounding effects of familiarity. Therefore, the present study was designed to clarify the effects of an individual's degree of familiarity with an odor on negative emotions experienced when dreaming.Methods: The airflow with phenylethyl alcohol (PEA: rose-like smell) was presented as a stimulus of experimental condition, and odorless airflow was presented as the control. Participants who were familiar (n = 7) and unfamiliar (n = 7) with the odor of PEA experienced both conditions during REM sleep in the second and later sleep cycle. Then, they were awakened, and they rated the characteristics of their dream using a questionnaire.Results and Conclusions: Participants who were familiar with the odor of PEA rated their dreams more negatively in the experimental condition relative to the control condition. It is concluded based on these results that a familiar odor may induce negative emotion in dreams, possibly because familiar odors tend to be perceived more strongly, and the olfactory pathway has direct connections to the amygdala, which is primarily involved in processing negative emotions. [ABSTRACT FROM AUTHOR]

Questionnaires on morningness-eveningness by Torsvall and Åkerstedt, sleep habits, psychiatric aspects and dreaming were administered to 870 students aged 12-15 years attending one of two junior high schools located in urban area in Kochi city (33°N) and suburban and neighboring area. Students who had negative dreams that were frightening, sad and so on tended to have later bedtimes and a shorter sleep duration and more frequently felt depressed or were unreasonably easily angered than those who had happy dreaming. A later bedtime may be related to a higher frequency of negative dreaming, which seems to trigger mental symptoms such as a depressed mood and irritation in Japanese adolescents. [ABSTRACT FROM AUTHOR]