Mental decline in old age turned out to be the property of the human body, which is not observed among chimpanzees.

A team led by Chet Sherwood (Chet Sherwood) from George Washington University (USA) suggests that mankind thus paying for longevity, acquired in the course of evolution.
"With regard to people the combination of large size of the brain, the neocortex is energetically costly (the upper part of the cerebral cortex) and high life expectancy increases the aging process ... In combination with other factors, this leads to the fact that many elderly people suffer from lower mental ability and dementia as a result of degeneration of nerve tissue "- the scientists say.

The authors measured the brain volume in 87 people aged 22 to 80 years and 99 chimpanzees (from ten to 51 years) by computed tomography. In addition to the total, biologists interested in the size of parts of the brain responsible for higher mental functions - gray and white matter of the frontal lobes and the hippocampus.

Scientists have found that for a person characterized by a "threshold of aging" for each area of ​​the brain. From a certain age, the aging process different parts of the brain are considerably accelerated. The fastest way to reach the threshold of the frontal cortex doltq - 57-58 years in cell "gray matter" begin to age rapidly. Least susceptible to aging hippocampus - the process of neuronal degeneration begins here close to 80 years.
On average, the elderly brain is reduced by 15-20% as compared with its volume in adolescence and adulthood.
Next of kin rights - the chimpanzee - retain their mental faculties almost until his death. Scientists note that the brains of older chimps 1-2% less than their younger compatriots. Tomography of the skull chimpanzees showed that the structure and volume of the frontal lobes and the hippocampus has not changed much.

As the authors of the article, the degradation of nerve cells in the brain can be caused by the accumulation of "problems" in the power plants of cells - the mitochondria. Mitochondria have their own DNA and errors when reading her age will cause energy "hunger" in the neurons. As a result, damage to cellular DNA, which leads to degradation of the nervous tissue and a significant weakening of mental abilities.