VIBROTACTILE THRESHOLD IS ELEVATED IN TEMPOROMANDIBULAR DISORDERS

Experimental pain can elevate vibrotactile threshold, a phenomenon att ributed in the literature to the operation of a 'touch gate.' It is no t known, however, whether clinical pain produces similar effects. To e xplore this possibility, we measured vibrotactile threshold in patient s with temporomandibular disorders (TMD) whose pain had a prominent my algic component. Two-interval forced-choice tracking was used to deter mine threshold for a 25-Hz vibratory stimulus presented on the cheek. Threshold was found to be significantly elevated in the TMD group, com pared to an age- and gender-matched control group of pain-free individ uals. Within the TMD group, those with a supra-median level of muscle tenderness (corrected for background levels of spontaneous pain) had s ignificantly higher threshold than those with lower levels of palpatio n pain. These findings are consistent with the idea of a touch gate, a nd suggest the usefulness of further research in this area with clinic al pain populations. The effects of an adapting stimulus (25 Hz, 20 dB SL) were also studied, and found to produce parallel elevations in vi brotactile threshold in the TMD and pain-free groups. This result indi cates that at least some adaptation occurs at a higher (subsequent) le vel of somatosensory information processing than does the touch gating implied by the unadapted thresholds.