Preferential responses on a positional recognition task in aged and young monkeys

The present experiment assessed learning and memory of five young and three aged monkeys in a spatial recognition task. Subjects were tested in a delayed non-matching to position (DNMP) task evaluating preferential response as well as accuracy of the task. There was no clear difference between the two age groups in the number of trials to reach the learning criterion. This result is consistent with the previous studies using non-spatial tasks. However, analysis of the process of learning revealed differential patterns in the emergence of preferential responses in both groups. While four patterns were observed in the young monkeys, in contrast, only one of the four was observed in the aged monkeys. The aged monkeys showed preferential responses in the early phase of learning, followed by rapid learning. This analysis of preferential response suggests that position preference behavior was effective in learning for the aged monkeys but not for the young monkeys. After reaching a criterion, the monkeys were subjected to longer retention intervals of 10-60 seconds. In this task, two aged monkeys performed as accurately as young monkeys did, while another one showed severe impairment. As has been shown previously for the non-spatial task, considerable individuality was found again in a memory task with the aged monkeys, with respect to spatial task as well.