Men lose brain tissue three times faster than women as they age, with the sharpest decline in the part of the brain that governs mental flexibility and attention span, according to a new study of brain activity.
The findings could partly explain why men die, on average, 10 years younger than women, said Ruben C. Gur, a psychologist and psychiatrist at the University of Pennsylvania Medical Center.
“I think it’s quite well-understood that men are more dispensable as they grow older,” he said. “This may be a mechanism to ensure that unneeded things don’t stay around.”
Would the loss of attention span also explain why many men are compulsive channel surfers? Gur declined to speculate.
The study, presented over the weekend at the annual meeting of the American Association for the Advancement of Science, is one of a number of efforts to find out why men and women don’t act alike.
For instance, men on average do better on tests requiring spatial orientation, while women are better at language. But the differences are so slight that there is no way to predict how a person of one or the other sex would perform, researchers say.
And it’s hard to separate what role genetics, the brain, hormones and the environment play in making us what we are.
“I have no qualms whatsoever about identifying biological differences between the genders,” said Jacquelynne S. Eccles, a psychologist at the University of Michigan who has spent 20 years studying the way boys and girls are raised.
What people should keep in mind, she said, is that “in this culture and in all cultures throughout the world, there is overwhelming evidence of different treatment starting at birth. Culture does not leave it to chance that men and women reach adulthood with different goals.”
Gur has spent eight years looking at the brains of healthy men and women with powerful scanning technologies such as Positron Emission Tomography, or PET.
With these machines, researchers can watch parts of the brain light up and become active as people talk, think or perform various tasks.
Men start out life with bigger brains than women, which makes sense because their bodies are larger, Gur said. But beginning at age 18, they lose brain tissue much faster, especially in the area known as the frontal lobe, which is responsible for attention span, planning and mental flexibility. By age 45, their frontal lobes are the same size as women’s.
As if to make up for this loss, men’s brains continue to work at a high metabolic rate.
Even when men are asked to relax during a brain scan, “they’re still overworking those parts of the brain that serve functions they perform well,” Gur said. For instance, a lawyer might use his frontal lobe to keep hashing over a case or an athlete might use the motor area of his brain to relive a performance.
When these brain cells are driven too hard and too long, he said, they can accumulate toxic waste products and die. This could explain why men’s brains deteriorate faster and, perhaps, why men die younger.
In contrast, women shift to various parts of their brains when they relax, and their overall brain metabolism slows as they get older, Gur said.
“Even though they, too, lose tissue as they age, they seem to be riding herd on what is left,” he said.
Gur said his findings don’t necessarily mean men are visibly falling apart as they hit middle age. The scanning techniques are so sensitive that “it’s conceivable we’re detecting changes that would not be necessarily noticeable in the workplace” or in other aspects of ordinary life.
Besides, Gur said, people also gain experience as they age, “and with experience, you need less of everything else.”