The Thermal Grill Illusion of Pain: Characterizing Differences in Response across Body Sites

The simultaneous application of interlaced innocuous warm and cool stimuli (a thermal grill stimulus, TGS) can elicit sensations of burning heat (the Thermal Grill Illusion, TGI). The TGS is thought to alter the central interactions between somatosensory sub-modalities (i.e. coldinhibition of pain). Previous psychophysical findings point to body site differences in perceptual thermal thresholds. The primary objective of this study was to evaluate whether, using the same TGS, a TGI can be elicited at body sites other than the upper extremity. The present findings indicate that the TGI can be induced at the palm, back, calf, and foot. Pain and unpleasantness in response to the TGS were more frequent and intense following stimulation of the palm and back than the calf and foot. Lower cold pain thresholds were associated with lower pain intensity ratings in response to the TGS. These two findings may reflect differences in central integrative processes.