Two groups of old monkeys, one group surviving radiition, the other group nonirradiated, were compared for changes in behavior accompanying aging. The 17 rhesus monkeys used as subjects in these experiments consisted of two groups, each comprised of 6 monkeys aged 8.0 to 9.0 yr, and survivors of another group which had received 1100 r of whole-body x rays in 3 doses of 400, 400, and 200 r spaced at yearly intervals. Subjects were trained in a Wisconsin General Test Apparatus (WGTA). The first experiment involved giving old irradiated and nonirradiated monkeys and young nonirradiated monkeys concurrent discrimination problems in a modified retroactive inhibition paradigm. In the 2nd experiment the technique of substituting less for more preferred rewards during intratrial delays was used to test the frustrative effects of substituting inferior rewards or eliminating rewards within trials. The third investigation was designed to determine whether monkeys could learn to shift set, and whether previously irradiated and nonirradiated monkeys could shift with equal facility. ln all these experiments only one finding in any way supported the hypothesis that chronic effects of radiation miniic aging effects. This was the superiority of the performance of the control group over the performance of subjectsmore » with a radiation history in original learning of concurrent discrimination problems in Experiment I. There were, however, several differences between the two groups of old animals not related to the hypothesis on aging, and all of these differences appear consonant with the known changes in behavior of monkeys following irradiation. These negative findings, together with the previous negative findings of the effects of irradiation on learning, suggest that the syndrome caused by irradiation is dissimilar both to the syndrome resulting from aging and the syndrome caused by circumscribed lesions of the central nervous system. The features seen in monkeys irradiated with either whole-body or cortical irradiation are motivational and perceptual. It is concluded that differences between the groups did not suggest that aging-like changes are the chronic consequences of radiation. (BBB)« less
Read full abstract