Mechanisms of pain relief by vibration and movement.

Mechanisms of pain relief induced by vibration and movement were investigated. A CO2 laser beam, which is useful for pure nociceptive stimulation, was used for recording pain-related somatosensory evoked potentials (pain SEPs) and for measuring pain threshold and reaction time (RT). Concurrently applied vibratory stimuli to and active movements of the fingers significantly reduced and prolonged pain SEPs, increased pain threshold, and prolonged RT, indicating that an increase in the inhibitory mechanisms of painful feeling was induced by the concurrently adopted sensory inputs mediated by large myelinated fibres. In contrast, continuous cooling enhanced pain SEPs and decreased pain threshold, probably due to the spatial summation of two kinds of nociceptive impulses mediated by the same pathways. The results of this investigation throw light on the mechanisms of the alleviation of pain by vibration and movement.