Impairments in acquisition and reversals of two-choice discriminations by aged rhesus monkeys

The ability to learn and perform reversals of two object, two patterns, and one spatial discrimination was examined in eight aged (28-34 years), and f our adult (8-13 years) behaviorally naive monkeys. As a group, the aged mon keys demonstrated significant difficulties in learning and reversing some o f the visual discrimination problems, but had no difficulty learning or rev ersing the spatial discrimination. Additional analyses revealed that an imp airment in learning an object discrimination by the aged monkeys was charac terized by a prolonged period of chance performance, and the impairments in performing visual discrimination reversals was related to difficulties in two distinct stages of reversal learning. Despite age-related differences, there was considerable variability in performance among the aged monkeys. T hese experiments provide the first evidence of significant impairments in l earning and reversing visual discriminations by aged monkeys that have not had prior exposure to complex behavioral tasks. (C) 2000 Elsevier Science I nc. All rights reserved.