Aging of the cerebral cortex differs between humans and chimpanzees

Abstract

Several biological changes characterize normal brain aging in humans. Although some of these age-associated neural alterations are also found in other species, overt volumetric decline of particular brain structures, such as the hippocampus and frontal lobe, has only been observed in humans. However, comparable data on the effects of aging on regional brain volumes have not previously been available from our closest living relatives, the chimpanzees. In this study, we used MRI to measure the volume of the whole brain, total neocortical gray matter, total neocortical white matter, frontal lobe gray matter, frontal lobe white matter, and the hippocampus in a cross-sectional sample of 99 chimpanzee brains encompassing the adult lifespan from 10 to 51 y of age. We compared these data to brain structure volumes measured in 87 adult humans from 22 to 88 y of age. In contrast to humans, who showed a decrease in the volume of all brain structures over the lifespan, chimpanzees did not display significant age-related changes. Using an iterative age-range reduction procedure, we found that the significant aging effects in humans were because of the leverage of individuals that were older than the maximum longevity of chimpanzees. Thus, we conclude that the increased magnitude of brain structure shrinkage in human aging is evolutionarily novel and the result of an extended lifespan.

Primate aging in the mammalian scheme: the puzzle of extreme variation in brain aging

“…These findings challenge earlier postmortem findings of 10% decrease of total brain weight in chimpanzees grouped as 15-30 vs. 30-59 years (Herndon et al 1998). Because the details of diet, infections, social environment, and other husbandry factors that influence brain development and aging are not known for this study, we consider the findings of Sherwood et al (2011) to be more definitive, pointing to the conclusion that chimpanzees have milder presentation of gross atrophic changes during aging than humans or shorterlived primates.…”

“…Regional atrophy of prefrontal cortex by MRI correlated with impaired spatial and recognition memory (Shamy et al 2011). However, a very recent MRI analysis of chimpanzees aged 10-46 years (N069; Yerkes National Primate Center) did not find any indication of atrophy in cerebral cortex, hippocampus, or white matter (Sherwood et al 2011). These findings challenge earlier postmortem findings of 10% decrease of total brain weight in chimpanzees grouped as 15-30 vs. 30-59 years (Herndon et al 1998).…”

Cortical cell and neuron density estimates in one chimpanzee hemisphere

“…The animal was humanely killed because of myocarditis (heart failure). The neocortex is expected to have few age-related changes in a chimpanzee of this age (51,52). Shortly before death, her body weight was 34.8 kg.…”

Comparative Pathology of Aging Great Apes

“…50 MRI of 69 living chimpanzees plus formalin-fixed brains from an additional 30 chimpanzees found no significant change in brain volume from ages 10 to 45 y and no decline in white matter volume. 232 A larger study consisting of MRI scans from 219 chimpanzees also showed little or no loss of volume and only mild loss of gray matter with aging. 20 Thus far, it seems that among the great apes, humans are unique in their capacity for brain shrinkage.…”