Response characteristics of cutaneous warm receptors in the monkey

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Abstract
Receptive elements to changes in tongue surface temperature, warm units, showed a steady-state discharge whose frequency was a function of the static skin temperature: a phasic increase in activity when the skin was warmed; a phasic decrease in activity when the skin was cooled; and little or no change in activity to mechanical stimulation, save for skin injury. The specificity of warm units to cutaneous thermal stimulation and their activity in the moderate physiological range of skin temperature suggest that they may contribute to thermal sensations, to thermal comfort and to body temperature regulation. Based on evidence derived from electrophysiological methods specifically sensitive primary warm afferents appear to exist in at least some of the cutaneous afferent nerves. Early reports of acitivity in warm units were mainly qualitative. Most studies report steady state discharges at static skin temperature between 30 and 45-48.degree. C with maximum activity between 40-45.degree. C; activity was observed in 1 monkey (Macaca mulatta) warm unit at static temperature as high as 57.degree. C. The steady state response of warm units to stimuli is discussed.