Temperature

Abstract

The concept that thermal sensations are elicited by stimulation of receptors uniquely responsive to warming or cooling has its origins from human studies performed in the 1880s. Quite independently, Blix, Goldscheider, and Donaldson (see Boring, 1942) demonstrated the presence of localized sensory spots on the skin, which when properly stimulated, produced sensations of warmth or cold. The topography of such spots has been described in detail for most parts of the body and the highest densities occur on the face, particularly the lips (Hensel, 1973a). Intraoral spots have also been reported with highest densities in the anterior part of the mouth (Yamada et al., 1952). Cold spots in all areas seem to be distributed more densely than warm spots. It is not clear from the human data whether these “spots” represent discrete sensitive zones or areas of maximum sensitivity in more diffuse thermosensitive regions. However, recent electrophysiological data indicate that thermoreceptors usually have single-spot receptive fields less than 1 mm in diameter (Darian-Smith et al., 1973; Dubner et al., 1975; Hensel, 1973a) consistent with the concept of discrete sensitive zones.