Response characteristics of cutaneous cold receptors in the monkey

Abstract

Quantitative descriptions of the steady-state and dynamic responses of a population of primate cold receptors were made after their receptive fields were subjected to several intensities of cooling (-.DELTA.T) and warming (+.DELTA.T) at 2 rates of temperature change from adapting temperatures (AT) between 20-45.degree. C. These were averaged for each condition of stimulation to assist in the interpretation of patterns of activity recorded at higher levels along the temperature pathways in the CNS. The latency of response onset to -.DELTA.T remained relatively constant at 200-400 ms for AT up to and including 35.degree. C. At higher AT it increased sharply. The rate of increase in frequency of the dynamic response reached a maximum at the 30.degree. C AT for the fast -.DELTA.T, whereas it was at a maximum at the 20.degree. C AT and decreased as AT increased for the slower -.DELTA.T. The magnitude of the dynamic response as indexed by the peak response frequency, cumulative impulses in the first 4 s following stimulus onset, the average frequency during the stimulus and the total impulse during the stimulus all showed maximum sensitivity to -.DELTA.T from the 35.degree. C AT. (Stimulus is defined here as occurring during the time period of the change in temperature from the AT to a new level.) The peak response frequency invariably occurred prior to the end of the stimulus (-0.5.degree. and 1.0.degree. C changes at the fast rate excepted). Of the units, 30% showed pardoxical responses to -.DELTA.T from the 45.degree. C AT, i.e., cooling suppressed the steady state response and warming to the 45.degree. C AT produced a phasic burst of activity.