Attention, executive functioning and memory in normal aged rhesus monkeys

Understanding how cognition declines in normal aging is vital in order to distinguish between normal cognitive decline due to aging and cognitive decline due to an age-related pathological process such as Parkinson's disease (PD). Several cognitive domains including memory, executive functioning and attention are all adversely affected with age in humans, as well as by PD, yet less is known about how these processes are affected by aging in non-human primates. Thus, in order to characterize baseline performance in aged primates prior to inducing Parkinson-like pathology, male rhesus macaques aged 15-22 years were tested on several tasks analogous to those used in cognitive aging studies in humans. The tasks included simple visual discrimination to assess learning and reference memory, discrimination reversal to assess cognitive flexibility and response inhibition, continuous performance to assess sustained visual attention, and attention set shifting to assess cognitive flexibility and set-shifting ability. Deficits were detected in some aspects of learning, cognitive flexibility, response inhibition and sustained visual attention, whereas reference memory and set-shifting did not appear to be affected. Additionally, there was a greater amount of variability in cognitive abilities across the aged animals than observed previously in young adult animals. These findings will form an important baseline for comparison with cognitive performance after PD-like pathology is superimposed on the normal aging process.