Researcher Chet Sherwood, holding a chimpanzee brain
“We are very weird animals,” said Emory University anthropologist Todd Preuss at the Yerkes National Primate Research Center in Atlanta, who wasn’t involved in the study. “Among neuroscientists, the assumption has been that species are all the same, but this shows there is something really unusual about the late-life biology of the human species.”
It’s estimated that as much as one in every five people in the US will be over the age of 65 by 2030, more than twice the number of elderly just a decade ago, according to the US Administration on Aging. Unfortunately for us, unlike chimpanzees and other primates, elderly humans are vulnerable to a host of neurodegenerative diseases such as Alzheimer’s–the hope of researchers is that understanding the basic biology of the brain can lead to new treatment and measures to postpone the mental demise of aging.
In this study, the first direct comparison of humans to chimps, a team of brain-scanning scientists led by George Washington University anthropologist Chet Sherwood find that chimps don’t experience such memory loss and that humans are uniquely afflicted by this oddity of longevity. They used MRI technology to scan and measure changes in five crucial brain structures involved in memory, reasoning and mental processing, and overall brain volume and density. Measurements were compared from 87 adult human brains (that’s, ahem, a lot of brains) ranging from 22 – 88 years of age with brain volumes of 99 adult chimps ranging from coinciding 10 – 51 years of age. The gray matter of neurons and white matter of connecting neural fibers were also measured. Chimps’ brains were found to only weigh a third as much as the average 3 lb human brain. The 3 lb human brain was found to shrink by up to a surprising 15% in later years.
The results? “We found no age-related changes in chimpanzees,” said Dr. Sherwood. The human brains lost significant volume over time while the chimpanzees’ remained intact with age. But what humans eventually won’t have in brain volume, they make up for with longevity– a human being can expect to live up to 80 years or more, almost twice the normal lifespan of a chimpanzee in the wild.
“It seems that this is the cost,” said Dr. Sherwood. “We experience more extensive atrophy in the brain that results in this obvious shrinkage, of a kind that is not seen even in our closest relatives, chimpanzees.”
“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,” said Sherwood. “It was already known that macaque monkeys, separated from humans by about 30 million years, do not show humanlike, widespread brain atrophy in aging.”
“This is an excellent example of research that has implications for societal benefits,” said NSF Physical Anthropology Program Officer Kaye Reed. “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.”
Hotz, Robert L. “Brain Shrinkage: It’s Only Human.” The Wall Street Journal | Health. Dow Jones & Company, Inc, 26 July 2011. Web. 30 July 2011. http://online.wsj.com/article/SB10001424053111903999904576468224286877908.html.