Scientists at George Washington University in St. Louis scanned a sample of 99 adult chimpanzee brains ages 10 to 51 years, measuring total volume and the volume of certain regions, MedicalNewsToday.com reported Tuesday.
They compared those measurements with scans of 87 adult humans ages 22 to 88 years.
While the volume of brain structures in chimpanzees did not shrink much as they aged, there was a measurable decline in the sizes of all the brain structures measured in humans, they said.
"Although other animals experience some cognitive impairment and brain atrophy as they age, it appears that human aging is marked by more dramatic degeneration," Chet C. Sherwood, a professor of anthropology, said.
The strongest effects in humans were found in individuals who were older than the maximum longevity of chimpanzees, who normally don't live past their 45th birthday in the wild, the researchers said.
"Thus, we conclude that the increased magnitude of brain structure shrinkage in human aging is evolutionarily novel and the result of an extended lifespan," the researchers said.
The team was particularly interested in the hippocampus, an area of the human brain that suffers the most damage in Alzheimer's disease.
Human may be vulnerable to Alzheimer's disease because we have more pronounced brain atrophy than other primate species, even when we age normally and healthily, the researchers said.
Humans have evolved to possess a large brain and a very long lifespan.
"While there are certainly benefits to both of these adaptations, it seems that more intense decline in brain volume in the elderly of our species is a cost," Sherwood said.