**5. Conclusion**

er, the sensation is not perceived as a powerfully unpleasant experience (Principles of Neu‐ ral Science, 2000a). Furthermore, the anatomical connections between the amygdala and the temporal (cingulate gyrus) and frontal (prefrontal) association cortices provide the means by which visceral and somatosensory sensations trigger a rich assortment of associations or the

**Figure 7.** Pathways responsible for somatosensory information in the brain. Somatosensory information evoked by vibrotactile stimulation is relayed by the trigeminal sensory complex and solitary and parabrachial nuclei, which arrive at the hypothalamus, thalamus, amygdala, and frontal cortex, respectively. The autonomic system (particularly the parasympathetic nervous system) produces increased salivation. The lateral branch of the trigeminal sensory nucleus projects to the parabrachial nucleus. Information from the parabrachial nucleus is received by the amygdala and fron‐ tal cortex. Furthermore, somatosensory information is projected to the primary somatosensory cortex and relayed to the frontal cortex via the parietal association area. Thus, this information finally leads to a relaxed feeling, and BBF waves reflect parasympathetic activity (modified from schemas in Principles of Neural Science 2000b and Handbook of

Neuropsychology 1994).

cognitive interpretation of emotional states (Principles of Neural Science, 2000b).

366 Advances in Vibration Engineering and Structural Dynamics

We showed that the most effective changes in salivation, pupil contraction, and HRV modu‐ lation (RR interval) were elicited by 89 Hz-S vibrotactile stimulation on the face. We thus conclude that 89 Hz-S vibrotactile stimulation affected parasympathetic activity based on changes observed in three organs. We also investigated autonomic activity by observing fNIRS waves. Because increased salivation was only observed in the submandibular and sublingual glands, it was likely not due to hunger. Furthermore, pupil constriction due to 89 Hz-S stimulation was less than that due to light following the resting condition. This likely indicated parasympathetic activity induced by 89 Hz-S stimulation. Changes in heart rate (RR intervals) during various stimuli were as effective as changes due to various stimuli combined with the 89 Hz-S stimulation. BBF oxyHb concentrations in the frontal cortex dur‐ ing 89 Hz-S vibrotactile stimulation were the same as those in subjects who preferred listen‐ ing to classical music. Thus, 89 Hz-S vibrotactile stimulation may produce relaxation; salivation increases, pupil diameter constricts, and the heart rate (RR interval) is prolonged due to parasympathetic excitation. Thus, we believe that fNIRS in the frontal cortex reflects autonomic activity.
