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The implications of male and female brain differences: A discussion

Men and women are equal, but they and their brains aren’t the same, according to a growing pile of scientific evidence. So why is most research still performed on only male animals and men? A panel of researchers explored this question and its implications on a recent episode of KALW’s City Visions radio show.

“It’s important to study sex differences because they are everywhere affecting everything,” said panelist Larry Cahill, PhD, a professor of neurobiology and behavior at the University of California, Irvine. “Over the last 20 years in particular, neuroscientists and really medicine generally have discovered that there are sex differences of all sizes and shapes really at every level of brain function. And we can’t truly treat women equally if we continue to essentially ignore them, which is what we’ve been doing.”

Neuropsychiatrist and author Louann Brizendine, MD, went on to say that many prescription medicines are only tested on male animals and men, even birth control pills designed for women. This is because the researchers don’t want the fluctuations of hormones associated with the menstrual cycle to “mess up” the research data, she said.

However, this practice can lead to dangerous side effects for women, she explained. For example, the U.S. Food and Drug Administration determined that many women metabolized the common sleep aid, Ambien, more slowly than men so the medication remained at a high level in their blood stream in the morning, which impaired activities like driving. After reassessing the clinical data on Ambien, Brizendine said, the FDA reset the male dose to 10 mg and the female dose down to 5 mg.

Nirao Shah, MD, PhD, a professor of psychiatry and behavioral sciences and of neurobiology at Stanford, said this action by the FDA was a sign of progress. “Decisions like what were made about Ambien represent people starting slowly to wake up and realize that we’ve been assuming that we don’t have to worry fundamentally about sex. And in not worrying about it, we are disproportionally harming women. Bare in mind, women absolutely, clearly and disproportionally bear the brunt of side effects of drugs and medicine.” In fact, he explained, eight out of ten drugs are withdrawn from the market due to worse side effects in women. He later added, “This issue is deeply affecting medical health, especially for women.”

So why are most researchers still studying only male animals or men?

According to Cahill, researchers have a deeply ingrained bias against studying sex differences, believing that sex differences aren’t fundamental because they aren’t shared by both men and women. He also said that resistance to this research boils down to the implicit and false assumption that equal has to mean the same. “If a neuroscientist shows that males and females (be that mice or monkeys or humans) are not the same in some aspect of brain function, then [many people think] the neuroscientist is showing that they are not equal — and that is false.”

Cahill offered advice for consumers: “You can go to the FDA website and for almost any approved drug you can get the essentials on how the testing was done. You’re going to find a mixed bag. For some drugs, you’re going to find there is pretty darn good evidence that the drug probably has roughly equal effects in men and women. On the other hand, you’re going to find a lot of cases when the testing was done mostly or exclusively in males and basically people don’t know [the effects in women].”

"You should be discerning and do your homework," Brizendine agreed.

Previously: Inside the heads of men and women: A look at sex-based cognitive differencesExploring sex differences in the brain and Tomayto, tomahto: Separate genes exert control over differential male and female behaviors
Photo by George Hodan

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