Male and Female Brains Really Are Built Differently

The hemispheres of women's brains are more interconnected. Does that matter?

Warren Jorgensen / AP

Ready your knowing smirk, because here comes a scientific gem that’s sure to enliven even the dullest of holiday parties.

By analyzing the MRIs of 949 people aged 8 to 22, scientists at the University of Pennsylvania found that male brains have more connections within each hemisphere, while female brains are more interconnected between hemispheres.

Yes, take that, Mike from IT! It, like, so explains why you just dropped the eggnog while attempting to make flirty conversation with Janet from Accounting.

Just kidding; we still have no idea why men or women do anything in particular. But the study, released today in the Proceedings of the National Academy of Sciences, is interesting because it is one of the first to discover differences in the brain’s structural connectivity in a large sample size of people from a variety of age groups.

Male (upper) and female (lower) brain connections (PNAS)

By analyzing the subjects’ MRIs using diffusion imaging, the scientists explored the brains’ fiber pathways, the bundles of axons that act as highways routing information from one part of the mind to the other. After grouping the image by sex and inspecting the differences between the two aggregate “male” and “female” pictures, the researchers found that in men, fiber pathways run back and forth within each hemisphere, while in women they tend to zig-zag between the left, or “logical,” and right, or “creative,” sides of the brain.

Because female brains seem to have a stronger connections between their logical and intuitive parts, “when women are asked to do particularly hard tasks, they might engage very different parts of the brain,” said Ragini Verma, an associate professor of radiology at the University of Pennsylvania and one of the authors of the report. “Men might over-engage just one part of the brain.”

This could mean, for example, that men tend to see issues and resolve them directly, due to the strong connections between the “perception” and “action” areas of their brains, while women might be more inclined to combine logic and intuition when solving a problem.

Their less-interconnected hemispheres might prompt men, for example, to be, “going along, executing things very skillfully and maybe not taking into account that someone didn't [do something] because they were having a bad day,” Verma explained. Meanwhile, “gut feelings, trying to join the dots together … women are known to be very strong in that.”

The differences were less evident in young children, but they became prominent in the scans of the adolescents.

Child (B), adolescent (C), and adult (D) brains (PNAS)

Scientists have long known that male and female brains are distinct, but the degree of these differences, and whether they impact behavior, is still somewhat of a mystery. The field has repeatedly unearthed seemingly solid clues that turned out to be red herrings. In August, for example, a study in the journal PLoS One challenged the long-held idea that male and female brains exhibit differences in “lateralization,” or strengths in one half of the brain or another. And past books on the “male” and “female” styles of thinking have been criticized for only including studies that reinforce well-known gender stereotypes.

At the same time, there’s plenty of evidence that male brains are from Mars and female brains are, well, from a different neighborhood on Mars. Researchers already know, for example, that men’s brains are slightly bigger than women’s (because men’s bodies also tend to be bigger). Male and female rats navigate space differently. Women taking birth control pills, which alter estrogen and progesterone levels, have been shown to remember emotionally charged events more like men do in small studies. Migraines not only strike women more frequently, but they impact different parts of their brains, too.

A study published last month in the journal Nature Communications found that genes are expressed differently in men and women throughout the brain. One reason autism rates are higher among males, the researchers suggest, could be because a form of the gene NRXN3 is produced at higher levels in male brains.

And past research has shown that, across cultures, women’s brains are more functionally interconnected when at rest than men’s are, on average. This and similar findings have been used to support the idea that women are “better at multitasking.” And indeed, a study released late last month by researchers at the University of Glasgow in Scotland found that women do have an edge when it comes to switching between tasks rapidly, ostensibly because, back in the cave, we had to keep an eye on the kids while we ... did whatever else it is that cave housewives did.

But examining the brain differences between the sexes also has an ugly past, since such findings have historically been used to paint women as less rational or intelligent.

The 19th-century French anthropologist Paul Broca, who lends his name to the area of the brain responsible for speech, once said, "We are therefore permitted to suppose that the relatively small size of the female brain depends in part upon her physical inferiority and in part upon her intellectual inferiority.”

At the same time, though, modern medicine can’t afford to ignore these variations. Just as with any disease, understanding sex differences in brains might help neuroscientists better diagnose and treat disorders.

“We see these differences everywhere, and we started to realize, damn, we simply assume they aren't there,” Larry Cahill, a neuroscientist at the University of California at Irvine, told the Orange County Register. “And these sex differences have implications for how the brain works and how to fix brains.”

Even pain medications don’t take male and female pain perception differences into account, Cahill points out. Countless medical fields have long been treating women by pretending “they are simply men with pesky sex hormones.”

The most uncomfortable aspect of such findings is that they can be—and often are—twisted to prop up stereotypes and prejudices. Studies like the PNAS one might offer fodder for those who wish to explain away female underrepresentation in fields like engineering with factoids about brain “wiring.” (Something former Harvard president Larry Summers essentially once suggested.)

But of course, that kind of thinking leaves out culture, which plays a big role not only in shaping how we think—both inside and outside of MRI machines—but also in determining what we do with our brains, however they’re structured. Verma emphasized that there’s a great deal of variation between individuals. Different fiber-pathway configurations don’t necessarily predestine someone to behave or think a certain way.

“There is a lot to be said about the structural wiring of the brain,” Verma said, “but it's what you use the wiring for that changes the person that you are.”

Or as Anke Ehrhardt, a psychiatry professor at Columbia University Medical Center cautioned during a recent panel on neuroscience and gender, "Acknowledging brain effects by gender does not mean these are immutable, permanent determinants of behavior, but rather they may play a part within a multitude of factors and certainly can be shaped by social and environmental influences.”

Spoken like someone who has her intuition wired firmly to her logic.