Sex and Brain Science

Is the study of sex differences gaining traction in neuroscience? It was the topic of the very first Social Issues Roundtable at the Society for Neuroscience, in 1983, and it was the topic again this year. Thirty years ago, it didn't seem to affect the crowd, though—research continued to focus on males (usually excluding females, whose additional monthly cycles were sometimes thought to dirty the results and be too complicated to take into account).

But now, "I'm starting to believe we've hit some sort of critical mass in the past decade," said Larry Cahill of the University of California, Irvine. "I think it's going to start changing rapidly."

Cahill is in a position to know. He's been talking about sex differences in research for decades, often to deaf ears, he said. Sex differences in the brain are real, and critically important, but news and information about them often gets misinterpreted. Media and careless people often overgeneralize from close studies to the greater population, to the point where "male brains" and "female brains" can seem different species.

Cahill said he has heard people who would never generalize the results of male-only rat studies to female rats, then go on and generalize them to people—both men and women.

In terms of behavior research, too, "there is a tendency for people to light up all their gender schemas," said Melissa Hines of Cambridge University. Just because non-human mammals show sex-typed preferences when they play with toys doesn't mean human boys are doomed to a truck-fixation, for example. Data from people who have gender identity disorder suggests that people are affected by hormones, but also how they are raised and where they were raised (and when—pink was considered the "boy" color in the U.S. 100 years ago).

Nevertheless, "there are sex differences at all levels of brain function… down to the molecular level," Cahill said. For example, a manner of apoptosis (how cells die and are cleared away) differs by sex. Another recent robust finding is in how emotional memories are processed. "It's just ubiquitous in brain science," he said.

Different also does not mean unequal, Cahill argued. For example, would you say "2 plus 3" does not equal the very different "10 minus 5"? Male and female brains certainly have some differences, but the results they produce, in cognition and behavior, may well be equivalent.

"If two populations are different and you want to treat them equally, you may have to treat them differently," Cahill said.

"I'm also against the misconceptions at this meeting, and I know about them because I shared them," Cahill said. It is not too hard to take sex differences into account when planning research—all research takes differences into account. And it doesn't always make things more complicated: "I am unaware that the average effect size in sex difference research is any different than any other area of brain reseach," he said

"The real peril… is that people will continue not to study sex differences. For me, it means the burden of proof has shifted. It's up to you to justify why you're not taking it into acount," he told the scientists in the room.

Searching the SfN database for posters, workshops, and sessions including the term "sex+difference," I got more than 150 hits, including sessions on neural development, immunity, stress, memory, antidepressant response, and obesity. On the other hand, there were more than 16,000 posters and sessions presented during the meeting.

Also speaking during the roundtable were Janet Hyde of the University of Wisconsin and  Maryjane Wraga of Smith College; the event was organized by Lise Eliot of Chicago Medical School of Rosalind Franklin University of Medicine and Science. I had to leave for another lecture halfway through the roundtable's Q&A session, but I heard later it got a bit heated (see more on Slate and at Psychneuro's blog). 

–Nicky Penttila

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