Facial Vibrotactile Stimulation Activates the Parasympathetic Nervous System: Study of Salivary Secretion, Heart Rate, Pupillary Reflex, and Functional Near-Infrared Spectroscopy Activity

Abstract

We previously found that the greatest salivation response in healthy human subjects is produced by facial vibrotactile stimulation of 89 Hz frequency with 1.9 μm amplitude (89 Hz-S), as reported by Hiraba et al. (2012, 20011, and 2008). We assessed relationships between the blood flow to brain via functional near-infrared spectroscopy (fNIRS) in the frontal cortex and autonomic parameters. We used the heart rate (HRV: heart rate variability analysis in RR intervals), pupil reflex, and salivation as parameters, but the interrelation between each parameter and fNIRS measures remains unknown. We were to investigate the relationship in response to established paradigms using simultaneously each parameter-fNIRS recording in healthy human subjects. Analysis of fNIRS was examined by a comparison of various values between before and after various stimuli (89 Hz-S, 114 Hz-S, listen to classic music, and “Ahh” vocalization). We confirmed that vibrotactile stimulation (89 Hz) of the parotid glands led to the greatest salivation, greatest increase in heart rate variability, and the most constricted pupils. Furthermore, there were almost no detectable differences between fNIRS during 89 Hz-S and fNIRS during listening to classical music of fans. Thus, vibrotactile stimulation of 89 Hz seems to evoke parasympathetic activity.

Effect of Salivation by Facial Somatosensory Stimuli of Facial Massage and Vibrotactile Apparatus

“…The increase toward plus direction of OxyHb is associated with neuronal activities, but when we become sleepy, it is decreased toward below zero [12,13]. On the other hand, the zero level of OxyHb of fNIRS showed parasympathetic activity from our data [5][6][7]. According to the amount of OxyHb of fNIRS, OxyHb in the stranger massage showed the decrease below zero, as shown in Figure 5.…”

“…The sampling rate across all 16 channels was 0.76 Hz. In particular, we showed a 16-channel computerized analysis (as shown in the previous papers [5][6][7]) and the original waves of four channel recording areas in the central parts. Analysis of amount of OxyHb of fNIRS on the frontal cortex is examined by the program of fNIRS Data Viewer, and we explored channels 4, 7, 10, and 13 of the central part of the frontal cortex.…”

“…Apparatus of 89 Hz frequency and 9.8 μm amplitude vibrotactile stimulation was chosen by data of the previous papers [1,[5][6][7][8], as shown in Figure 1B-a, -b. We tried three vibrotactile stimuli, (89, 114, and 180 Hz, and others all of 9.8 μm amplitude), and the best salivation was 89 Hz frequency in comparison with others, as shown in Figure 2.…”

“…Analysis of amount of OxyHb of fNIRS on the frontal cortex is examined by the program of fNIRS Data Viewer, and we explored channels 4, 7, 10, and 13 of the central part of the frontal cortex. Data recorded by the experiment measured the value of integral of four channels in the center frontal cortex, and we calculated mean value of integral of four waves [5,6,10,11].…”

“…This increase in circulation also elevates the temperature around the gland which may activate acinus gland cells. Initially, we examined the effect of facial somatosensory stimuli by using of the apparatus of vibrotactile stimuli [1,[5][6][7][8]. Secondly, we tried to carry out hand massages, again.…”