Focal Mechanical Vibration Does not Change Laser-Pain Perception and Laser-Evoked Potentials: A Pilot Study

Background: Nonpainful tactile and electrical stimulation of the large myelinated fibers reduces spontaneous pain and the amplitude of laser-evoked potentials (LEPs), which represent the most reliable technique to assess the nociceptive pathway function. Focal mechanical vibration stimulates the Aβ afferents selectively; thus, it is conceivable its action on nociceptive pathways. Aim: The aim of this study was to investigate the effect of vibratory stimuli, activating either both muscle and skin receptors or cutaneous afferents only on the LEPs and subjective laser-pain rating. Methods: Ten healthy volunteers were studied. The subjects were evaluated in two different sessions to test muscle and skin receptors or cutaneous afferents only. In each session, LEPs were recorded to stimulation of the dorsal hand skin in radial and ulnar territory bilaterally, while the vibratory stimulus was delivered on the radial territory of the right forearm. Results: The results showed a substantial stability of the potential N1 and N2/P2 after the two protocols, with a declining trend from the initial to the last test of the same session, probably due to habituation. Accordingly, the laser-pain perception did not change during the experimental setting. Conclusions: We conclude that a vibratory stimulus is ineffective in reducing the laser-evoked potentials and laser-pain perception.