Effect of auditory and olfactory stimulation on prefrontal cortex for stress alleviation

In contemporary society, an increasing number of people have excessive stress which affects their physical and mental conditions. As for methods of alleviating stress, listening to music and aromatherapy can be cited. These are expected to be applied to complementary alternative medicine because they can be easily handled. However, the effect depends on sensory evaluation. In this study, oxygenated hemoglobin (Oxy-Hb) concentration in the prefrontal cortex was measured by applying auditory or olfactory stimulations to an organism during a time of rest and stress using near-infrared spectroscopy. (1) An experiment that applied rest and stimulation alternately and (2) an experiment that applied stress and stimulation alternately were conducted for 10 subjects (6 male and 4 female). During rest time, subjects were asked to repeat counting from 1 to 10. In experiments with auditory stimulation, three kinds of music with 1/f fluctuation were listened to by the subjects. In olfactory stimulation, three essential oils which are supposed to have a relaxing effect were inhaled. The stress time allowed subjects to perform one digit of mental arithmetic. The Oxy-Hb concentration change decreased with time when auditory stimulation in (1) and all stimulation in (2) were applied. In addition, the mean values of Oxy-Hb concentrations at rest, stress, and each stimulation were calculated, and the differences were compared to evaluate each stimulation. In the case of (1), Oxy-Hb concentration decreased at auditory stimulation time in comparison to rest time. Oxy-Hb concentration was confirmed to decrease in all stimulations in (2). Oxy-Hb concentrations in both experiments were compared using a t-test. Significant differences in Oxy-Hb concentrations were observed in the left prefrontal cortex for all the stimulations (p<0.05). Therefore, it can be suggested that the stimulations used in this experiment are effective in alleviating stress.