Jaw clenching modulates sensory perception in high- but not in low-hypnotizable subjects

Aims: To investigate the effect of jaw clenching on the sensations evoked at segmental and nonsegmental levels by painful and nonpainful stimuli and in relation to hypnotic susceptibility. Methods: The effect of jaw clenching on painful and nonpainful sensations on the face and leg was studied in high-hypnotizable (HH) and low-hypnotizable (LH) subjects. Sixteen healthy subjects were selected and assigned to either the HH group (n = 8) or the LH group (n = 8). Painful and nonpainful electrical stimuli were delivered in random order to the face and leg. The subjects rated the intensity of the evoked sensation on a visual analog scale (VAS) while clenching or not clenching their jaw. Results: Jaw clenching significantly attenuated the VAS sensory ratings of all the subjects under various conditions (F_1-31 = 6.15, P < .02). When the HH and LH subjects were analyzed separately, jaw clenching was found to be effective in reducing sensations only in the HH subjects (F _1-15 = 8.30, P = .01), only those evoked in the face (segmental level), and only those evoked by nonpainful stimuli (tied Z = 2.52, tied P < .02). Conclusion: Sensory modulation produced by jaw clenching may be related to hypnotic susceptibility. On the whole, jaw clenching had a weak, local effect in modulating sensation, in contrast to its known widespread effect on motor behavior.