Correlations of Temperature Sensation and Neural Activity: A Second Approximation

Abstract

Some 12 years have passed since our first attempt to relate changes in thermal sensations to changes in neural activity (KENSHALO 1976). and this is a timely opportunity to consider the progress that has been made since that first report. This particular relationship is but a part of a more general correlation between sensory and physical events, or in HERBERT HENSEL'S terminology, between phenophysics (psychophysics) and'phenophysiology (psychophysiology) (HENSEL 1982; HENSEL and KONErfZNY 1979). The aim here is to briefly review the actions of several stimulus variables known to have pronounced effects on the quality and magnitude of thermal sensations and to seek evidence of the effects of these same variables on the neural discharge at the levels of the primary afferents, second-order afferents in the spinal cord and medulla, the thalamus, and other central nuclei in the blAin stem, and finally the cortex. Special emphasis is placed on evidence of temporal as well as spatial facilitation at the several synaptic levels. Reviews of DAR IAN-SMITH (1984), HELLON (1983), and HENSEL (1981, 1982) have recently appeared that deal with several of these topics. 2.1.2 Psychophysics of Thermal Sensations Unlike the modalities of vision, audition, olfaction, and gustation, the thermal sensing system of the skin has but two, perhaps three, qualities of sensation-coldness, warmth, and perhaps heat, although evidence in support of the existence of a sense of heat as a unique quality is slight, at best. The reaction time and dissociation experiments of FRUHSTORFER (l976a) provide convincing evidence that the nerve fiber population engaged by warming the skin is different from that engaged by cooling it. It has been known for many years that the skin is not uniformly sensitive to temperature. When, for example, an area of skin is systematically explored with a