Male Vs. Female Brains: What’s the Difference?

The answer is key to what happens to each gender after a stroke

When neuroscientist Larry Cahill decided he wanted to study the differences between the male and female brain, colleagues told him that was a surefire way to kill his career.

For one, raising the possibility that male brains were different from female brains wasn’t exactly politically correct. More than a decade ago, Gloria Steinem reportedly told then-ABC reporter John Stossel that it’s “anti-American, crazy thinking to do this kind of research.”

Scientists also thought males were easier to study, because they didn’t have the so-called “complicating factor of a menstrual cycle,” says Cahill, a professor of neurobiology and behavior at the University of California, Irvine. They believed "you’re studying all the fundamental things of the female in the male, except in a cleaner way,” he adds.

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But they were wrong, Cahill says. Now, Dr. Francis Collins, director of the National Institutes of Health (NIH), would agree with him.

In the May 15 issue of the journal Nature, Collins and Dr. Janine Clayton, director of the National Institutes of Health’s Office of Research on Women’s Health, unveiled policies to ensure that cell and animal research considers females as well as males.

Sex Differences and Disease

The NIH already ensures that women are included in clinical research funded by the agency, a requirement mandated by Congress in 1993. Today, Collins and Clayton write, slightly more than half of participants in NIH-funded clinical studies are women. Yet, they write, “there has not been a corresponding revolution in experimental design and analyses in cell and animal research.”

And one of the main research areas in which sex differences are relevant is brain-related diseases, according to Collins and Clayton. They cite rodent research that suggests estrogen therapy might protect against multiple sclerosis and human research into how a particular drug lessens cravings for cocaine and alcohol in women but not in men.

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“People are finally starting to realize now that you just can’t study the male and assume you are understanding everything that’s fundamental in the female,” Cahill says.

Still, he says, he didn’t expect to see such a statement from the NIH leadership for another 15 or 20 years. “I almost can’t believe it,” says Cahill.

It’s no longer politically incorrect to acknowledge that men’s and women’s brains, while equal, are not the same, says Cahill, who published a paper on that subject last month in Cerebrum.

He talked with Next Avenue about how and why, in some ways, men’s brains are from Mars and women’s are from Venus. Highlights:

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Next Avenue: So what are the main differences between men’s and women’s brains?

Cahill: Research suggests that the two halves of the brain are more interconnected in women than in men. There’s evidence that women suffer less language impairment after a stroke on one side of the brain because they have language centers in both halves. That allows the healthy half of the brain to pick up some of the work of the damaged half.

The differences between the brains of men and women are best conceptualized as two different complex mosaics — similar in many respects, different in others.

What’s behind the differences?

People used to assume that nurture, not nature, led to sex differences in the brain. But how people are raised can’t explain the differences seen in animals or in human fetuses in the womb. And the differences don’t increase with age and experience, meaning they must have been there all along. There is no doubt that circulating hormones explain many, but not all, sex differences.

Since their brains are different, doesn’t it make sense that there are certain jobs for which men or women are better-suited than members of the opposite sex?

It is logically reasonable to think so, at least on average, and at least for certain occupations that tap into the largest differences. But I think it is too early to say anything definitive. And in the end, it would boil down to individual strengths independent of sex, I suppose.

Who’s smarter: men or women?

On average, men’s and women’s IQs are equal. However, some studies suggest that men’s IQs cover a wider spectrum than women’s. In other words, it appears that men are more likely than women to have either high IQs or low IQs. 

Rita Rubin is a former USA Today medical writer who now writes about health and science for publications including Next Avenue, WebMD and NBCNews.com.

By Rita Rubin
Rita Rubin is a former USA Today medical writer who now writes about health and science for publications including Next Avenue, U.S. News, WebMD and NBCNews.com.@ritarubin

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