Thermal sensibility and thermoreceptors

Abstract

The sensing of changes in skin temperature is important in contributing to the total sensory information about an object making contact with the skin, and in assessing body heat loss or gain, that occurs over a large part of the body surface. These functions depend on resolution of small, local, shifts in skin temperature, and effective spatial summation by the central nervous system of thermal stimulus information. Aδ cold fiber populations excited uniquely by cooling the skin and unmyelinated warm fibers excited only by warming the skin constitute the 'labeled lines' that signal all the immediate information available to the brain about changes in skin temperature. The authors have correlated the capacity of human subjects to identify incremental differences within pairs of warming or cooling temperature pulses and the neural events evoked by similar stimuli in the cutaneous nerve fiber populations of monkeys (Macaca nemestrina). The conclusions are that human discrimination of incremental changes in skin temperature depends on information coded at the single fiber level as cumulative impulse count or rate over an integration interval of about 2 sec, the brain using information signaled by all the thermoreceptive fibers engaged by the stimulus, the dependent variability among fibers of the responding population being slight, and the brain integrating this information by some method of 'weighted' averaging, which biases the process to favor those fibers that most effectively relay stimulus information.