Coding of steady and transient temperatures by cutaneous "cold" fibers serving the hand of monkeys

Much of the neurophysiological data obtained from rapidly cooled skin surfaces can be related to the mean frequency of discharge in single cold fibers; mean frequency data obtained during steady skin temperatures are less informative. The deterioration of the frequency code during steady temperatures parallels the deterioration in psychophysical measurements of sensations of cold. However, small differences of steady skin temperature alter thermoregulatory responses demonstrating the central availability of detailed information about steady temperatures, even though the mean frequency of the individual cold fiber's adapted discharge lacks this information. Another parameter of the single fiber's response, the temporal arrangement of impulses, provides sufficient information during steady temperatures to account for published data on thermoregulatory responses. Thus the organization of the impulse pattern in cold fibers may constitute an additional code capable of conveying information about steady skin temperature centrally.