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 the reverse effect: Heat at levels that induce pain can substantially suppress tactile sensitivity, independently of shifts in attention or arousal. Ten human observers were stimulated by a tonic, pain-producing heat stimulus and vibrotactile stimuli (1, 10, and 100 Hz) coincidentally presented to the right thenar eminence. Vibrotactile thresholds were assessed with the skin at a normative temperature of 31 degrees C and at higher temperatures producing pain. Increases in vibrotactile thresholds (mean change = 7.3 dB) occurred at skin temperatures just below and above those that induced pain. Furthermore, absolute-magnitude estimates of suprathreshold vibrotactile stimuli determined during the same experiments showed decreased sensitivity and psychophysical recruitment. The changes are not attributable to attentional or arousal shifts, since they were not associated with changes in auditory thresholds. Furthermore, the changes occurred just below the subjects' pain thresholds (where nociceptors are presumably activated). This over-twofold diminution of vibrotactile sensitivity suggests that heat stimuli capable of inducing pain can significantly diminish taction, perhaps through a "touch gate" in a manner similar to the gate control theory proposed for pain.