Executive system dysfunction occurs as early as middle-age in the rhesus monkey.

As our understanding of age-related cognitive decline advances, studies are now focusing on identification of those areas of cognitive function that undergo the first changes with age. In the present study, in order to determine whether executive function is sensitive to the aging process, we assessed the performance of 16 monkeys of middle-age (12-19 years of age) on the conceptual set-shifting task, an analogue of the Wisconsin Card Sorting Test (WCST). We compared their performance to that of seven young adult (5-9 years of age) and 18 aged monkeys (20-30). The findings showed that middle-aged monkeys, like those of advanced age, were significantly impaired on the conceptual set-shifting task (CSST). These findings parallel those of recent studies in humans demonstrating an increase in perseverative errors on the WCST by middle-aged as well as aged individuals and, in turn, support the notion that disruption of executive function is one of the earliest changes in cognition to occur in normal aging.