Modification of human pain threshold by specific tactile receptors.

The effects of conditioning vibrotactile stimulation of particular tactile receptor groups on thresholds to painful electric stimuli were studied in seven healthy adults. Preferentially Pacinian afferents were activated with conditioning sinusoidal vibration of 240 Hz at 20 and 200 micrometers amplitudes and preferentially non-Pacinian tactile fibers were activated with conditioning sinusoidal vibration of 20 Hz at 200 and 400 micrometers amplitudes. None of the subjects showed pain threshold elevation during activation of non-Pacinian tactile fibers. However, 6 of the 7 subjects showed significant pain threshold elevation with conditioning vibration stimulus of 240 Hz at 200 micrometers amplitude, and 4 subjects showed significantly elevated pain thresholds with conditioning stimulus of 240 Hz at 20 micrometers amplitude. It is concluded that the activation of Pacinian afferents causes inhibition of pain conducting pathways.