Response latencies of rats during behavioral thermoregulation

Abstract

The cutaneous thermal stimulation that elicits behavioral thermoregulatory behavior was investigated in these experiments. In Experiment I, rats were placed in a cool environment and allowed to barpress for 3-sec bursts of radiant heat reinforcement. In various phases of the study, rats could earn different intensities of anterior, posterior, or whole-body radiation. Identical response rates were exhibited at each intensity for all exposure conditions; this information, when considered with existing literature on behavioral and neurophysiological studies, suggests that the rat's thermoregulatory behavior depends on information carried by nonmyelinated fibers that supply thermoreceptors in the skin. Experiment II investigated the hypothesis that cooling of the skin is the stimulus that elicits each thermoregulatory response. Time series measures of skin temperature fluctuations and reaction times (RTs) were obtained. Tails of the RT distributions were shown to conform to exponential probability density functions, and mean RT varied linearly over the domain of reinforcement intensities used. A computer simulation model that describes temperature gradients across layers of skin was employed to estimate temperature fluctuations at the level of the cool receptors. Comparison of simulated skin temperatures with obtained RTs suggests that momentary thermoregulatory behavior is controlled mainly by cooling skin temperature.The cue that controls responses in behavioral thermoregulation is still unknown, although many aspects of the ability of animals to maintain normal body temperature in cold environments have been studied (Carlisle, 1970;Corbit, 1970). It is well known that a fall in skin temperature is necessary for initiation of behavioral thermoregulation (Weiss & Laties, 1961;Carlisle, 1966Carlisle, , 1968, but a question remains concerning the stimulus utilized by the animal when each operant response is emitted. Several possibilities exist: the animal can work (appetitively) for heat or it can work to avoid or escape cold.A discussion by Carlisle (1970) concluded that heat intake occurs at a constant rate as a function of reinforcer duration and intensity when the former parameter is under control of the animal. He was not able to specify the sensory function that controlled the behavior, but could only assume that some temperature-dependent signal arising from on or within the animal was involved. A model was presented by Corbit (1970) intended to account for available data on thermoregulation:In this model, Thy 0 and TSo are temperatures of the hypothalamus and skin, respectively, that fail to elicit thermoregulatory behavior and may be considered as the core temperature and skin temperature of the rat measured at 20°-2SoC. They are relatively constant throughout the experiment, so that behavior is mainly During behavioral thermoregulation, the sequence of response-reinforcement pairs causes T. to fluctuate more rapidly, and throughout a greater range, than variations in T. o ' Thus, T. is more likely to serve ...