July 26, 2011

Human Brain Different Than Chimps As It Shrinks With Age

Researchers say that evolution of human longevity led to both a large brain and brain shrinkage.

A team of researchers sought to find out if a chimpanzee brain shrinks as much as a human's brain does with old age.

Chet Sherwood, an anthropologist at The George Washington University in Washington, D.C., and a team of scientists from seven other U.S. universities used magnetic resonance imaging (MRI) to measure the space occupied by various brain structures in adult humans and chimpanzee.

They found chimpanzees do not display significant loss in the size of their brains and other internal structures as they age.

Sherwood and colleagues found that as humans evolved the ability to live longer, the result was a "high degree of brain degeneration" as people get older.

"We were most surprised that chimpanzees, who are separated from humans by only 6-8 million years of independent evolution, did not more closely resemble the human pattern of brain aging," Sherwood said in a press release. "It was already known that macaque monkeys, separated from humans by about 30 million years, do not show humanlike, widespread brain atrophy in aging."

Both humans and chimpanzees develop and age on different schedules, so the study compared humans from age 22 to 88 and chimpanzees from the age 10 to 51. 

The researchers 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 chimpanzees and 87 adult humans.

"Traits that distinguish humans from other primates include enlargement of the brain and increased longevity," they wrote in the report "Aging of the Cerebral Cortex Differs Between Humans and Chimpanzees."

They said humans are unique among animals in being susceptible to certain neuropatheologies, like Alzheimer's disease.

"This is an excellent example of research that has implications for societal benefits," NSF Physical Anthropology Program Officer Kaye Reed said in a press release.

"While Dr. Sherwood and colleagues are interested in the evolutionary significance of brain differences between chimpanzees and humans, the results of this research can be used as a basis to explore degenerative brain diseases, such as Alzheimer's, in a medical context."

The research, which was partially funded by the National Science Foundation, was published in the Proceedings of the National Academy of Sciences (PNAS).


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