To characterise cutaneous thermoreceptors, it seems essential to define exactly the conditions of thermal stimulation, more precisely the physical parameters of the stimulus and the thermophysical properties of the skin. Three experimental procedures of heat transfer to the skin are examined. The first procedure represents the ideal situation of a skin at a given base temperature suddenly out in contact with a thermode at a fixed temperature. The second procedure represents a situation in which the skin is put in contact with a thermode producing a linear heat ramp. The third procedure represents a situation in which the skin is exposed to a radiant heat source of constant energy density. The results of these studies show that neglecting the relationship between parameters of the thermal stimulus and the thermophysical properties of skin may lead to apparently paradoxical observations. In contrast, when properly controlled, these parameters can allow to vary considerably the delay between the arrival at the first spinal relay of information conveyed by A∂ and C-fibres and as a consequence allow to study their interactions. Finally, it seems that a source of radiation in the far infrared (CO<inf>2</inf> laser) offers several advantages over conventional heat stimulators.
Plaghki, L., & Stouffs, P. (2001). Biophysique de l’échauffement cutané par conduction et par radiation: Implications pour l’étude différentielle des afférences Aδ et C chez l’homme. Douleur et Analgésie, 14(1), 67-72. https://doi.org/10.1007/BF03007512 (Original work published 2001)