SOME DIFFERENCES IN EXTINCTION BY NORMAL AND WHOLE-BODY IRRADIATED MONKEYS.

Abstract

An extinction criterion was sought which would differentiate irradiated and normal monkeys. Four normal and 16 whole-body irradiated male rhesus monkeys used were the survivors of a study of radiation effects conducted 5 yr earlier. The estimated total dosages received from a mixed gamma and neutron radiation source were 0, 77, 154, 308, and 616 rep. The Wisconsin General Test Apparatus was used for testing. The stimuli for testing were two wooden test objects differing in multiple dimensions, and each monkey was tested for 24 trials on discrimination of the food-rewarded stimulus from the stimulus that was consistently nonrewarded. During the last 10 trials, the median errors for the control and irradiated groups, respectively, were l and 0, the mean median response latencies were 17.1 and 20.2 millimin, and the median frequencies of response latencies as large or larger than 50 millimin were 0 and 0. There was no significant difference with respect to each of these three variables in the two groups. During extinction, the irradiated monkeys achieved response latencies of 50 millimin or more faster than did the controls. The irradiated monkeys had more response latencies at or above 50 millimin than did the controls. Monkeys of themore » two higher radiation dosage groups had a comparable number of response latencies at or beyond the extinction criterion and more than those of the low- dose group. The data support a hypothesis of facilitation of extinction by exposure to radiation. These findings reflect another facet of the increased concentration of attention of irradiated monkeys, which facilitates the perception of any change associated with the site of food reward. They are consistent with earlier results which have shown facilitation of acquisition and retention accruing to radiation exposure, and extend the realm of facilitative effects of radiation exposure to include extinction. (BBB)« less