The influence of psychological state on the masseteric exteroceptive suppression reflex and somatosensory function

Objective This study examined the somatosensory function in the trigeminal region and quantitative measures of the exteroceptive suppression (ES) period in the masseteric EMG, in relation to a psychological evaluation. Methods The ES in the surface EMG was recorded from the left masseter muscle in 12 men and 12 women. The stimulation intensity at which the ES appeared first and the lowest intensity at which the subjects reported it to be painful were defined as the electrical reflex threshold and electrical pain threshold, respectively. Three experimental sessions were scheduled. The state and trait anxiety inventory was used to evaluate the psychological status. Results The electrical reflex threshold significantly decreased (p < 0.01), and the electrical pain threshold significantly increased (p < 0.01) over the sessions in line with the effect on the state anxiety inventory (p < 0.05). Conclusions The present results illustrate that reflex parameters and electrical pain thresholds are associated with state anxiety. Possibly, habituation or decreased fear from the experimental set-up may play a role. Significance This is important when electrophysiology or quantitative sensory testing is used to assess trigeminal nociception, e.g., in orofacial pain conditions.