Abstract:Humans can detect and discriminate a vast number of odours. The number perceived as distinguishable is estimated to be more than ten thousand. Humans are capable of distinguishing even slight alterations in the structure of an odorous molecule. A pair of enantiomers of an odorant, which possess the same molecular structures except for the chiral position, can trigger profoundly different odour perceptions. How precisely can humans and their olfactory system detect and discriminate such a great variety of odours and such subtle differences in the molecular structures? In a series of studies, we have attempted to examine the relationship between mood change, odour and its physiological effects, by focusing on the possible verbal and non-verbal changes in humans induced by smelling the fragrances of essential oils as well as linalool and its enantiometric isomers. In this article, we provide an overview of our recent verbal and non-verbal studies. We then discuss how our findings may contribute to the assessment of psychophysiological responses of essential oils as well as how our research can contribute to the study of human chemoreception science, by shedding light on the sophistication of the olfactory system in its ability to detect and discriminate odors.

To elucidate the psychophysiological effect of inhaling essential oils, in this paper, we sought to assess the following 12 essential oils: basil, bergamot, cardamom, cinnamon, juniper, lemon, orange, palmarosa, peppermint, sandalwood, spearmint, and ylang ylang. As these being target odors, we focused on the verbal (semantic) and non-verbal (skin temperature) endpoints of the stimuli. In our experimental design, we managed to assign different behavioral tasks to the participants. The Uchida-Kraepelin test was used as a mental arithmetic task and listening to environmental (natural) sounds as an auditory task. In the verbal study, for an example, we conducted the sensory test twice, once before and once after the task. As a measure of the perceived odor quality in participants after inhalation of a given aroma, we employed a sensory evaluation spectrum. It is a bar graph in which the mean of the difference in score between pre-and post-task inquiry (post minus pre) was plotted against the impression descriptors. Taking into account of the obtained skin temperature changes between pre-and post-task inhalations, the subtle nuances between verbal and non-verbal expressions seen as a function of the two behavioral tasks assigned to the participant suggested that essential oils may have versatile psychophysiological potencies by the nature.