Topographical distribution of warmth, burning and itch sensations in healthy humans
To gain information on the topographical distribution of warmth, burning and itch sensations in healthy humans, we delivered laser stimuli to elicit sensations of warmth, applied capsaicin cream for burning, and pricked histamine for itch on the skin of the face, shoulder, hand, thigh and foot in 12 healthy subjects. We found that whereas warm and burning sensations progressively increased from foot to face, itch sensation increased from face to foot (P<0.0001). Hence our findings indicate that unlike thermal and pain receptors, itch receptors are denser at distal than at proximal body sites. Our psychophysical study provides new information supporting the idea that specific unmyelinated neuronal pathways mediate sensations of warmth, burning and itch.