HEAT-INDUCED PAIN DIMINISHES VIBROTACTILE PERCEPTION - A TOUCH GATE

The gate control theory of pain (Melzack and Wall, 1965) suggests that tactile stimuli can decrease the perception of pain. We have found th e reverse effect: Heat at levels that induce pain can substantially su ppress tactile sensitivity, independently of shifts in attention or ar ousal. Ten human observers were stimulated by a tonic, pain-producing heat stimulus and vibrotactile stimuli (1, 10, and 100 Hz) coincidenta lly presented to the right thenar eminence. Vibrotactile thresholds we re assessed with the skin at a normative temperature of 31 degrees C a nd at higher temperatures producing pain. Increases in vibrotactile th resholds (mean change = 7.3 dB) occurred at skin temperatures just bel ow and above those that induced pain. Furthermore, absolute-magnitude estimates of suprathreshold vibrotactile stimuli determined during the same experiments showed decreased sensitivity and psychophysical recr uitment. The changes are not attributable to attentional or arousal sh ifts, since they were not associated with changes in auditory threshol ds. Furthermore, the changes occurred just below the subjects' pain th resholds (where nociceptors are presumably activated). This over-twofo ld diminution of vibrotactile sensitivity suggests that heat stimuli c apable of inducing pain can significantly diminish taction, perhaps th rough a ''touch gate'' in a manner similar to the gate control theory proposed for pain.