The effects of stimulus location on the gating of touch by heat- and cold-induced pain

The influence of heat- and cold-induced pain on tactile sensitivity, a "tou ch gate", was measured under conditions in which the location of the noxiou s stimuli was varied with respect to the tactile stimulus applied to the th enar eminence of humans. Vibrotactile thresholds were measured in the absen ce of pain and during administration of a painful stimulus, with the stimul us frequencies selected to activate independently the four psychophysical c hannels hypothesized to exist in human glabrous skin. Heat-induced pain pro duced by spatially co-localizing the noxious stimuli with the tactile stimu li was found, on average, to elevate threshold amplitude by 2.2 times (6.7 dB). Go-localized, cold-induced pain raised the average thresholds by about 1.5 times (3.6 dB). Heat-induced pain presented contralaterally produced n o change in vibrotactile sensitivity indicating that the effect is probably not due to attentional mechanisms. Ipsilateral heat-induced pain caused an elevation in tactile thresholds even when the noxious and non-noxious stim uli were not co-localized, and the effect may seem to require that the pain ful stimulus be within the somatosensory region defined possibly in terms o f dermatomal organization. Thus the effect is probably related to somatotop ic organization and is not peripherally mediated. A brief discussion as to the possible locus of the touch gate within the nervous system is also give n.