The afferent fiber population mediating the thermal evoked response to skin cooling in man

Abstract

A population of cold-responding fibers with response properties similar to those innervating primate skin were determined to be mediating the thermal evoked response to skin cooling in man. Cerebral evoked responses to a 10°C cooling pulse were recorded from human scalp at a 29°C adapting temperature where primate cold-responding fibers possess a considerable dynamic sensitivity. No time-locked cortical responses were reliably recorded from the 40°C adapting temperature to the same cooling pulse. At 40°C, thermally sensitive mechanoreceptors mediated by Aβ and large Aδ fibers possess their maximal sensitivity. In primate skin, specifically sensitive cold receptors are innervated by the small Aδ fiber group. The results of this study, then, suggest the existence of a small myelinated fiber group in human radial nerve, implying that the difficulty in recording from these fibers directly using microneurographic techniques in humans involves technical-morphological considerations. The results have implications for the utility of the cerebral evoked response technique as a clinical diagnostic tool, and the organization and representation of cortical temperature information in humans.