The current study sought to examine differences in physiological responses to comfortable thermal stimuli applied to the soles of the feet during the simultaneous presentation of other sensory stimuli. As relaxing stimuli, underwater movie footage, classical music, light blue illumination, vibration of the trunk, and the odor of grapefruit oil were each presented simultaneously with a thermal stimulus. Electroencephalography of parietal and cerebral blood flow in the prefrontal cortex were measured. An increase in α-wave activity and a decrease in cerebral blood flow were found for all combinations of stimuli compared with baseline. Additionally, the results revealed differences in response speed depending on the stimulus presentation condition. However, the tendency suggesting a difference in response times depending on the stimulus condition was similar to that of the thermal stimulus alone. The results indicated that thermal stimulation has a substantial effect on the feeling of relaxation.

We examined the degree to which relaxation was induced by the presentation of a comfortable thermal foot stimulation paired with other sensory stimuli. We presented a movie of an underwater scene, classical music, light blue illumination, vibrations to the trunk, and grapefruit odor as relaxing stimuli in combination with thermal stimulation, and measured physiological responses of the autonomic nervous system (electrocardiogram, respiration, fingertip pulse wave, peripheral blood flow, and sweating). All stimulus combinations induced parasympathetic activation compared with an initial control. In particular, the presentation of an odor with thermal stimulation elicited a remarkable degree of parasympathetic activation. We verified differences in the latency and duration of physiological responses depending on the stimuli combination. However, subjective relaxation was not confirmed, and parasympathetic activation for combined stimuli did not remarkably differ from that for thermal stimulation alone. These results indicate that thermal stimulation has a powerful effect on relaxation induction.