THE EFFECT OF HIGH AMBIENT TEMPERATURE ON TIMING BEHAVIOR IN RATS

Abstract

The present experiments demonstrated a reliable within‐session increase in rectal temperature (T re ) at 25° C during stable differential‐reinforcement‐of‐low‐rate (DRL) performance. The thermal response was found to be independent of the DRL value and reinforced DRL performance, but dependent on the state of the animal's deprivation. Exposure to a 35°‐C environment increased the post‐session T re significantly above the 25°‐C post‐session T re for seven of eight subjects. Response and reinforcement rate at 35° C was found to be independent of DRL value, although it decreased as DRL value increased at 25° C. A discriminative stimulus used to mark the end of the interval increased the reinforcement rate at 25° C but provided no advantage at 35° C. Measurement of the pattern of responding during DRL performance revealed increases in the proportion of long interresponse times at 35° C. Reinforcement rate was found to decrease progressively at 35° C, reaching a minimum within 40 to 50 min of the 90‐min session. Visual observation of overt behaviors during DRL performance at 35° C revealed a reduction in the frequency of overt behavior, characteristic of 25°‐C performance, and a time‐dependent increase in the probability of an alternative set of behaviors.