Facial vibrotactile stimulation activates the parasympathetic nervous system: study of salivary secretion, heart rate, pupillary reflex, and functional near-infrared spectroscopy activity.

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 μ m amplitude (89 Hz-S), as reported by Hiraba et al. (2012, 20011, and 2008).