THE THERMAL GRILL ILLUSION - UNMASKING THE BURN OF COLD PAIN

In Thunberg's thermal grill illusion, first demonstrated in 1896, a se nsation of strong, often painful heat is elicited by touching interlac ed warm and cool bars to the skin. Neurophysiological recordings from two classes of ascending spinothalamic tract neurons that are sensitiv e to innocuous or noxious cold showed differential responses to the gr ill. On the basis of these results, a simple model of central disinhib ition, or unmasking, predicted a quantitative correspondence between g rill-evoked pain and cold-evoked pain, which was verified psychophysic ally. This integration of pain and temperature can explain the thermal grill illusion and the burning sensation of cold pain and may also pr ovide a basis for the cold-evoked, burning pain of the classic thalami c pain syndrome.