Men suffer rapid brain shrinkage

Men chronically overwork some regions of their brains, leading to deterioration and shrinkage by early middle age. Women, on the other hand, keep more of their brain cells as they get older, according to Professor Ruben Gur, from the University of Pennsylvania.

Although men begin life with larger brains than women on average - reflecting their larger body size - they lose brain tissue at three times the rate of women. The differences are evident even between the ages of 18 and 45, relatively early in life and before hormonal changes associated with the menopause could come into play.

Professor Gur reported his findings to the association's annual meeting in Baltimore. Other researchers pointed out that for many years animal studies had revealed gender differences between the brains of males and females. These structural differences were sometimes related to behavioural differences, according to Professor Arthur Arnold, of the University of California at Los Angeles. He cited the case of songbird species where only the males sing courtship songs. The area of the brain governing singing is five times larger in males of such species compared to females.

However, Professor Jacquelynne Eccles, from the University of Michigan, warned that such information should not be misinterpreted when it came to human beings. "There are lots of reasons why humans differ from each other," Professor Eccles said.

Professor Gur conducted brain scans of the rate at which glucose is burned up in the brain and scans to measure the volumes of the brains. He studied 24 women and 37 men. "Women seem to be able to reduce the rate of neuronal (brain cell) activity in proportion to the tissue they lose, whereas men continue to overdrive their neurons," he said.

Part of the reason women live longer than men could be their ability to reduce metabolism in their brains because "if you overdrive cells, you get cytotoxic [cell killing] effects".

Men lose brain cells faster than women particularly in the frontal lobe area, which is responsible for mental flexibility, abstract reasoning and inhibition. "Men lose tissue in the frontal lobe at such a rate that by the time they reach middle age, even though they start with bigger brains, their frontal lobe is the same size as in women," Professor Gur said. "Women show almost no reduction in the brain volume in this region."

Professor Eccles stressed that research into gender differences did not suggest any policy decisions about the way society should treat males and females. She warned: "We should be cautious about taking evidence of average differences as the grounds for policy decisions about how to train and educate boys and girls."