The human brain is great, and it is powerful, able to imagine innovative solutions to complex problems. Yet, our brains do not age well: As we grow older, they tend to shrink and become increasingly vulnerable to cognitive impairments such as memory loss and dementia. A new magnetic resonance imaging (MRI) study comparing humans and chimpanzees found that chimps brains maintain their size as they age. slowly lose our minds, it is, perhaps the price changes we pay for having bigger brains and longer life.
Regarding the researchers can tell, humans are the only animals subjected to specific brain diseases such as Alzheimer's disease, which affects the United States nearly 50% of people aged over 85. But even normal, apparently healthy human brains showed the effects of aging, such as the accumulation of amyloid-beta plaque deposits and loss of neural connections, particularly in areas related to learning and Memory. And previous studies of human brains have suggested that these brain regions, which include the frontal lobe and the hippocampus, are especially prone to shrinkage with age.
Although few similar studies of other primates were conducted, recent research rhesus monkeys have shown that the very limited shrinkage with age. Nonetheless, the evolutionary lineages leading to humans and rhesus monkeys diverged there are about 30 million years, leaving scientists in the dark when the human model brain aging could have started.
For a better idea, a team led by Chet Sherwood, an evolutionary neuroanatomist at George Washington University in Washington, DC, directly compared the brain-shrinking chimps and humans schemes, which have diverged are only about 5000000 to 7000000 years. The study sample consisted of 87 humans ranging from ages 22-88, and 69 chimpanzees from 10 years to 51. As chimpanzees rarely live more than 45 years in the wild, although some in captivity survived in their 60s represents the sample at the normal lifetime of these two species.
The team used MRI scanners to measure the size of a number of brain regions in humans and chimpanzees. The differences are striking: Although chimpanzees showed no significant age-related shrinkage in one of the measured regions, all regions of the human brain have shown dramatic effects of age, reports the online team this week in the Proceedings of the national Academy of sciences . Some regions have decreased to 25% in 80 years. Furthermore, the tendency was somewhat different for the human gray matter, which contains the body of the nerve cells and their nuclei, as well as auxiliary cells such as microglial cells and human white matter, which consists of long axons neural and making connections between the various brain regions.
For example, the gray matter of the human frontal lobe shrank on average by about 14% between the ages of 30 and 80, and gray matter in the hippocampus by about 13% in the same period. But the withdrawal of the white matter was even more severe. The white matter of the frontal lobe decreased by approximately 24%, similar to white decrease in the volume of the material in most other brain regions measured
In addition, unlike the gray matter, which showed a gradual withdrawal over time, the decline in white matter was steepest between the ages of 70 and 80. Thus, although the average decline in the frontal lobe was 24% at 80 years, it was only about 6% to 70 years.
Why are chimpanzees throughout their normal life cover without significant shrinkage of the brain, whereas the human brain seems to wither with age?
"This is the question a million dollars," said Sherwood. In the paper, the team points out that the greatest human brain, which is more than three times larger than that of a chimpanzee, also energy demand much higher. Thus, the human brain uses up to 25% of the total available energy of the body when we are at rest, compared to no more than about 10% for other primates.
the record track with what energy supplies, the team argues, appears on the cellular and molecular levels in the human brain. this includes a decline in mitochondrial efficiency, energy storage of living cells, as well as damage caused by oxidative stress, the result of molecules containing oxygen that are produced during cellular metabolism.
"My guess is that our neurons essentially do the best they can to keep the maximum operating for as long as possible, "said Sherwood. "But they have the chance really stacked against them after years of high energy consumption."
Dean Falk, an anthropologist at the Advanced Research School in Santa Fe find the differences between gray and white matter material models particularly interesting withdrawal. White matter, humans have relatively more as chimpanzees and other primates, "is particularly important for complex cognition Homo sapiens ," Falk said, because it makes the connections between brain regions involved in the transmission of information in problem solving and other complex tasks.
Nevertheless, Peter Rapp, a neurobiologist at the National Health Laboratory of Experimental Gerontology Institute in Baltimore, Maryland, who conducted some of the earlier brain imaging studies in rhesus monkeys, indicates that the new study does not distinguish between brain shrinkage as a result of normal aging in humans and that the withdrawal could be due to the neuro-degenerative disease of the brain of a subset of subjects. "Is what distinguishes humans and chimpanzees susceptibility to disease, or a qualitative difference in the brains of aging in good health?"
Bruce Yankner, a neurologist at Harvard Medical School in Boston, agrees. to test the hypothesis of the authors that the narrowing of the human brain is the result of greater longevity, Yankner said, "it would be interesting" to see if similar brain shrinkage occurs in other species with extreme longevity, "as turtles and tortoises that live for more than 100 years, elephants can live for 70 years, and parrots that can live for 80 years. "
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