Effects of selected aroma compounds on physiological activities and emotions

Abstract

Current literature has revealed the effects and therapeutic properties of a wide variety of aromatic compounds but studies on the inhalation effects of single aromatic compounds in terms of central nervous system, emotional states and autonomic nervous system are still very limited. So, this study aimed to examine the physiological and emotional effects of selected volatile compounds inhalation namely d-borneol (BO), d-camphor (CH), methyl eugenol (ME), methyl chavicol (MC) using scientific techniques on autonomic nervous system (ANS), self-evaluated questionnaire on emotional states and brain wave activities. Sweet almond oil was used as a carrier oil and a diluent control. This research was an experimental study using pretest-posttest design. The Ethical Review Committee from Chulalongkorn University approved this study with permissions No. COA No. 074/2020. Volunteers who were willing to participate in this study submitted a written consent form before participating in the study. A total number of 96 healthy participants (males and females) aged between 20 and 35 years were recruited and divided into 4 groups (24 participants in each group). ANS parameters including systolic, diastolic blood pressures, heart rate, respiratory rate and skin temperature were recorded. The questionnaires on emotional states measured subjective feelings of the participants. EEG was used to record brain wave activities. Data were analyzed using paired sample t-test by using SPSS statistical package version 22. A p-value <0.05 was considered significant. The Shapiro-Wilk test was used for the normality test. The results showed that the general characteristics of all the participants within each group were similar. In BO group, BO inhalation increased systolic blood pressure, diastolic blood pressure and heart rate significantly. BO inhalation increased good, fresh, active, romantic feelings significantly but decreased bad, annoyed, stressed, frustrated and disgusted feelings significantly. BO increased the beta wave over the left and right posterior brain areas significantly. In CH group, CH inhalation decreased systolic blood pressure, diastolic blood pressure, respiratory rate, heart rate significantly while increasing skin temperature. CH inhalation increased relaxed, calm feelings significantly but decreased active feelings significantly. CH inhalation increased the alpha wave power at all the brain regions namely left anterior, right anterior, center, left posterior and right posterior significantly. In ME group, ME inhalation decreased systolic blood pressure and diastolic blood pressure, heart rate and respiratory rate significantly. ME inhalation increased drowsy feelings significantly but decreased active and fresh feelings significantly. ME inhalation increased both the delta wave in left anterior, right anterior significantly and the theta wave in left anterior, right anterior and center significantly. In MC group, MC inhalation decreased systolic blood pressure, diastolic blood pressure, heart rate and respiratory rate significantly. MC inhalation increased relaxed feelings significantly but decreased bad, frustrated feelings significantly. MC inhalation increased the alpha wave in most areas namely left anterior, right anterior, center, and right posterior significantly. In conclusion, d-borneol was the only selected volatile compound with stimulating effects while the other selected volatile compounds namely d-camphor, methyl eugenol and methyl chavicol seemed to possess sedative effects through inhalation in healthy participants.