Differential effects of ionizing radiation on the acquisition and performance of response sequences in rats

To compare the effects of ionizing radiation on the acquisition and performance of response sequences, rats responding under a multiple schedule of food reinforcement were each administered 0.5-6 Gy of 60Co gamma radiation. In one component of the multiple schedule, subjects acquired a different three-response sequence each session by responding sequentially on one of three response keys in the presence of three consecutively presented colors (repeated acquisition). In the other component, the three-response sequence was the same each session (performance). The response sequence in each component was maintained by food presentation under a second-order fixed-ratio (FR) 2 schedule. Errors in both components produced a 5-sec timeout but did not reset the sequence. In all subjects, 0.5-6 Gy of gamma radiation dose-dependently decreased response rates in both components for 1-5 days postexposure. These gamma-ray doses also produced dose-dependent increases in errors in both components, but only at doses that substantially decreased response rate. Unlike the effects on response rate in both components, which were comparable over the 5-day period after exposure, the effects on accuracy were generally different for the two components. More specifically, the largest increases in percent errors in the performance component occurred on day 2 postexposure, whereas the largest increases in percent errors in the acquisition component occurred on day 4 postexposure. Taken together, these results indicate that (1) acute sublethal doses of gamma radiation differentially affect the acquisition and performance of response sequences, (2) these doses of gamma radiation differentially affect the measures of rate and accuracy within each condition of behavior, and (3) using a sensitive baseline, which includes an accuracy measure, provides important information about the disruptive effects of radiation that could not be predicted from the effects on response rate alone.