Neuropsychology of cognitive aging in rhesus monkeys

Abstract

Aged rhesus monkeys, like aged humans, show declines in cognitive function. We present cognitive test data from a large sample of male and female rhesus monkeys, 34 young (3.5-13.6 years) and 71 aged (19.9-32.5 years of age at the start of cognitive testing). Monkeys were tested on spatiotemporal working memory (delayed response), visual recognition memory (delayed nonmatching-to-sample), and stimulus-reward association learning (object discrimination), tasks with an extensive evidence base in nonhuman primate neuropsychology. On average, aged monkeys performed worse than young on all three tasks. Acquisition of delayed response and delayed nonmatching-to-sample was more variable in aged monkeys than in young. Performance scores on delayed nonmatching-to-sample and object discrimination were associated with each other, but neither was associated with performance on delayed response. Sex and chronological age were not reliable predictors of individual differences in cognitive outcome among the aged monkeys. These data establish population norms for cognitive tests in young and aged rhesus monkeys in the largest sample reported to date. They also illustrate independence of cognitive aging in task domains dependent on the prefrontal cortex and medial temporal lobe. (181 words).

Figure 1.

Delayed response performance across delay testing phase. Heavy lines indicate group means and standard errors, disaggregated by age and sex. Trace lines indicate performance of individual monkeys.

Figure 2.

Delayed non-matching-to-sample performance across delay testing phase. Heavy lines indicate group means and standard errors, disaggregated by age and sex. Trace lines indicate performance of individual monkeys.

Figure 3.

Object discrimination performance. Heavy lines indicate group means and standard errors, disaggregated by age and sex. Trace lines indicate performance of individual monkeys.

Figure 4.

Task performance separated by “unimpaired” / “impaired” subgroups of aged monkeys based on DR (left column) or DNMS (right column) performance. Subgroups based on DR do not differentiate performance of aged monkeys on DNMS or OD, whereas subgroups based on DNMS differentiate performance of aged monkeys on OD but not DR. Heavy lines indicate group means and standard errors. Trace lines indicate performance of individual monkeys.