Afferent modulation of warmth sensation and heat pain in the human hand

The hands of 14 normal humans were used to determine the somatotopic organization of the modulation of warmth sensation and heat pain by different forms of cutaneous stimuli. Test stimuli were 5-sec heat pulses ranging from 36 degrees to 51 degrees C, delivered to the fingerpads of digits 1, 2, 4, and 5 with a contact thermode. Conditioning stimuli (15 sec) bracketed the test stimuli and included vibration, noxious and innocuous heat, cold, and electrical pulses delivered to the fingerpads of digits that were adjacent or nonadjacent to the tested digits. Noxious (48 degrees +/- 1.3 degrees C), but not innocuous (43 degrees C), heat stimuli increased the perceived magnitude estimation of innocuous test stimuli (36-43 degrees C) by 20-37% when delivered to adjacent, but not to nonadjacent, digits. No other conditioning stimuli had any effect on the intensity of warmth perception. In contrast, both noxious and innocuous heat or electrical conditioning reduced the magnitude estimation of noxious (50-51 degrees C), but not innocuous, test pulses by 12-22% when delivered to adjacent digits. Conditioning of nonadjacent digits was significantly less effective. The analgesic effects of noxious and innocuous conditioning were approximately equal. Vibratory (120 Hz, 3.5 microns) and cold (15 degrees C) conditioning stimuli were ineffective. The results are consistent with a dermatomal somatotopic organization of tactile and heat modulatory influences on warmth sensation and heat pain. The results further suggest that the neural mechanism subserving warmth mediate a negative feedback influence on heat pain intensity.