Efficacy of vibration in reducing pain of experimental and clinical origin

The mechanisms involved in vibratory analgesia, the perceptual phenomenon in which vibrotactile stimulation can eliminate or reduce pain sensations, were examined in three experiments. Experiment 1 tested the ability of different frequencies of vibration, all equated in sensation level above threshold, to decrease the detectability of a phasic, thermal noxious stimulus utilizing signal detection theory methodology. Data analysis revealed that vibration was able to significantly decrease detectability of the noxious stimulus, and that this decrease was not dependent on frequency, as has been suggested in the literature. The second experiment utilized the same parameters of vibrotactile stimulation to test the effect vibration had on subject's ratings of pain due to a tonic, mechanical noxious stimulus. Like the results of Experiment 1, this second experiment showed that vibration was able to reduce pain in a frequency-independent manner. The final experiment examined the ability of two vibrations, a low- (20 Hz) and a high- (100 Hz) frequency, to significantly reduce the spontaneous pain associated with TMD. This experiment, unlike Experiments 1 and 2, showed that the high-frequency vibrotactile stimulus was effective at altering the spatial and temporal properties of clinical pain while the low-frequency stimulus was no different than a no-vibration condition. Together, the three experiments confirmed the robustness of vibratory analgesia, as tested on three different types of pain. The difference in the frequency-specificity of the effect in Experiment 3 compared to Experiments 1 and 2 is suggested to be due to differences in vibrotactile processing occurring on the forearm of normal, healthy subjects (Experiments 1 and 2) and those occurring on the face of subjects with TMD (Experiment 3).