Age‐ and cognition‐related differences in the gray matter volume of the chimpanzee brain (Pan troglodytes): A voxel‐based morphometry and conjunction analysis

Several primate species have been shown to exhibit age‐related changes in cognition, brain, and behavior. However, severe neurodegenerative illnesses, such as Alzheimer's disease (AD), were once thought to be uniquely human. Recently, some chimpanzees naturally were documented to develop both neurofibrillary tangles and amyloid plaques, the main characteristics of AD pathology. In addition, like humans and other primates, chimpanzees show similar declines in cognition and motor function with age. Here, we used voxel‐based morphometry to examine the relationships among gray matter volume, age, and cognition using magnetic resonance imaging scans previously acquired from chimpanzees (N = 216). We first determined the relationship between age and gray matter volume, identifying the regions that declined with age. With a subset of our sample (N = 103), we also determined differences in gray matter volume between older chimpanzees with higher cognition scores than expected for their age, and older chimpanzees with lower than expected scores. Finally, we ran a conjunction analysis to determine any overlap in brain regions between these two analyses. We found that as chimpanzees age, they lose gray matter in regions associated with cognition. In addition, cognitively healthy older chimpanzees (those performing better for their age) have greater gray matter volume in many brain regions compared with chimpanzees who underperform for their age. Finally, the conjunction analysis revealed that regions of age‐related decline overlap with the regions that differ between cognitively healthy chimpanzees and those who underperform. This study provides further evidence that chimpanzees are an important model for research on the neurobiology of aging. Future studies should investigate the effects of cognitive stimulation on both cognitive performance and brain structure in aging nonhuman primates. Regions of increased gray matter volume in cognitively healthy chimpanzees (compared with those that underperform for their age) that typically decline with age. Research Highlights Age is negatively correlated with gray matter volume in chimpanzees, revealing gray matter loss with age in regions similar to those identified in humans and macaques. Chimpanzees that perform better on cognitive tasks for their age have greater gray matter volume in several brain regions compared with those who perform worse for their age. A conjunction analysis revealed that cognitively healthy chimpa