A Comparative Study of Aging and Cortical Folding in Chimpanzees and Olive Baboons

In light of the evidence that nonhuman primates naturally develop Alzheimer's disease neuropathologies, there is a renewed interest in research on the comparative biology of aging, including neurological changes across the age groups in species with diverse lifespans. In this paper, we examined age-related differences in two measures of cortical folding, mean depth and fold opening, in a sample of chimpanzees (Pan troglodytes) and olive baboons (Papio anubis). We found significant species differences in the slope and pattern of age-related changes in cortical folding. As predicted, chimpanzees showed negative linear associations between age and mean depth and positive linear associations between age and fold opening, as we see in humans. However, contrary to our hypotheses, baboons showed positive quadratic associations between age and mean depth and negative quadratic associations between age and fold opening. Additionally, within the baboons but not the chimpanzees, significant sex differences were found in age-related differences in cortical folding. Here, male baboons showed significant linear associations between age, sulci depth, and fold opening, much like male and female chimpanzees. However, for female baboons, slopes of age-related differences in fold opening were flat or showed slight quadratic associations. It is possible that variation in primate social systems and/or reproductive aging may influence sex and species differences in brain aging. Longitudinal studies on primate brain aging, as well as comparative research with additional taxa, could shed light on the causes and implications of these differences.