Special to ABCNEWS.com
Women have smaller brains than men. Since the ability to think is partly determined by the size of the brain, men must be smarter than women, right?
Wrong, wrong, wrong. Men and women consistently score equally well on intelligence tests, despite the difference in brain size.
Neuroscientists have grappled with that puzzle for years. All kinds of research have shown that the bigger the brain, generally, the smarter the animal, although other factors affect intelligence.
Now a team of researchers from the University of Pennsylvania has come up with an explanation for the brain-size mystery. It’s not just the size, but what’s inside.
The researchers subjected 80 volunteers (40 men and 40 women, ages 18
to 45) to 3-D magnetic resonance imaging. The high-tech brain scan revealed
notable differences in the proportions of some key components inside the
female and the male brain.
It’s What’s Inside That Counts
Of special interest was the amount of “gray matter,” the part of the brain that allows us to think. The researchers wanted to know if women have as much gray matter as men.
“You find no difference in the amount of gray matter,” says Ruben Gur, professor of psychology at the University of Pennsylvania and the lead author of a study that appeared in the May 15 issue of the Journal of Neuroscience.
To make up for the smaller brains, women have 55.4 percent gray matter vs. 50.8 in men. The average brain weight of an adult male is 49.5 ounces — just over 3 pounds — while women typically have a 44-ounce brain, a one-third-pound difference.
Elsewhere upstairs though, men have far more “white matter,” which transfers information between distant regions — the key to spatial abilities.
That discovery helps explain some fundamental differences between men and women, the researchers say. While women seem to excel at verbal tasks and are just as smart as men, men are more adept at spatial tasks — knowing where they are in relation to the world around them. (Which may explain why men are loathe to ask for directions.)
Men don’t have just a little more white matter; they have a lot more. “When we looked at the top performers for spatial tasks in our study,there were nine men and only one woman,” Gur says. “Of these nine men, seven had greater white-matter volumes than any of the women in the study. This suggests that, in order to be a super performer in that area, one needs more white matter than exists in most female brains.”
Head and Shoulders Above the Rest
Gur says that’s the kind of thing that can set a super athlete apart from the rest of the herd.
“Spatial abilities are a big part of sports,” he says. A great soccer player always knows where he (or she) is in relation to the other players.
“It’s not just how big your muscles are and how fast you can move your legs,” he says. “It’s knowing where to go with all that speed.”
Star athletes may not be great at calculus, but they know how to maneuver on the field.
One of Gur’s collaborators is his wife, Raquel, who is a professor of psychiatry and neurology at the University of Pennsylvania.
She notes another difference between male and female brains. Previous research has shown that as the amount of brain tissue increases, cognitive performance improves. But this research shows that’s especially true for women.
“Women’s brains appear to be more efficient than men’s in the sense that an equal increase in volume produces a larger increase in processing capacity in women than in men,” she says.
Her husband thinks that may partly be because the female brain is smaller. A compact brain, Gur says, may simply be more efficient.
To see if more gray matter really mattered, the researchers gave their subjects standardized spatial and intelligence tests. Try these two questions they used:
Sailor is to Navy as soldier is to: a) gun b) cap c) hill d) Army. If you answered anything but Army, head for the soccer field. And this one, which even Gur admits is a bit tricky: Thoughts are to brains as steam is to: a) water b) vapor c) boiling d) heat. Scroll to the bottom of the page to see if you’re right.The Incredible Shrinking Brain
Researchers at the Henry Ford Health System reported recently that the male brain shrinks faster with age than the female brain. By using magnetic resonance imaging, the researchers measured brain size in 330 healthy men and women over the age of 66.
Shrinkage was most pronounced around the frontal and temporal lobes which control thinking, planning and memory.
The researchers aren’t sure what that means, but they think it could have a bearing on the differing losses of function through aging for men and women.
“We have known for a while that men tend to be more prone to age-related brain disorders, such as memory loss and Alzheimer’s disease,” says C. Edward Coffey, chairman of Henry Ford’s Department of Psychiatry. “These findings may help provide an explanation for these sex differences.”
Gina "Nanogirl" Miller
"Nanotechnology: solutions for the future."