Impairment in abstraction and set shifting in aged rhesus monkeys.

Understanding the nature of changes in cognition with aging has increased in importance as the number of individuals over the age of 65 years grows. To date, studies have demonstrated that age-related changes occur most extensively in the cognitive domains of memory and executive function. Whereas a large number of studies have been conducted about the effects of aging on memory, far less have explored the effects of aging on the so called "executive function" which include abilities essential for successful performance of higher level activities of daily living. As part of our ongoing effort to better characterize these changes, we assessed executive function in a non-human primate model of normal human aging using the Conceptual Set Shifting Task (CSST). This recently developed task assesses abstraction, concept formation and set shifting in the monkey in a way analogous to the Wisconsin Card Sorting Test (WCST) in humans. Relative to young adult monkeys, aged monkeys evidenced significant difficulty in both acquisition and performance on this task, and moreover, demonstrated a high degree of perseverative responding. The pattern of performance displayed by the aged monkeys suggests an age-related decline in prefrontal cortex (PFC) functioning.