Two years ago, a study of the differences between male and female brains caused a storm. The researchers, based at the University of Pennsylvania, claimed to have found that, from adolescence onwards, men’s brains have more connections within each hemisphere, whereas women’s brains have more cross-connections between the hemispheres — a finding which would support the idea that men’s and women’s brains work differently in important ways. In the press promotion for the research, the neuroscientists argued that their results helped explain past research suggesting that men are, on average, better at some mental tasks, such as navigating, while women are better at others, like being intuitive.
The study was widely criticized. Other experts pointed out that the sex differences in brain wiring were tiny, and anyway, the researchers hadn’t actually measured their participants’ mental abilities, so the argument that the brain wiring could explain gender differences in cognitive strengths was speculative. And unhelpful. The mass media extrapolated wildly from the findings to claim scientific proof for outdated gender stereotypes. Another thing: Even if the results were robust, the sex-based brain differences could be the result of cultural pressures — the participants in the study ranged in age from 8 to 22, but the gender effect only kicked in from 14 and upwards (which also, it should be said, leaves open the possibility that the differences are at least partially biological, but only kick in at puberty). In any event, the results certainly didn’t provide nearly as robust evidence for “innate” or “hardwired” sex differences as some mistaken journalists implied.
Now the same UPenn research team — including the senior husband-and-wife partnership of Raquel Gur and Ruben Gur — are back with a new brain-scan study published in the prestigious journal Cerebral Cortex, in which they make fresh claims about sex-based differences in mental abilities being rooted in the brain.
Whereas the research from 2013 used a technique called Diffusion Tensor Imaging to plot the white matter pathways of people’s brains — these pathways being the main way that information is channeled from one neural network to another — this new research used a different approach known as Resting State fMRI to uncover patterns of functional connectivity. Each participant lies in the scanner doing nothing other than staring at a cross on a screen, and from the participant’s resting neural activity, the researchers deduce a kind of map showing which brain areas are in communication with each other and the intensity of this communication.
The new research involved hundreds of participants between the ages of 9 and 22, and, unlike in the researchers’ previous experiment, this time the participants completed tests of mental ability, as well as having their brains scanned. Here, the researchers did find sex differences in mental ability — male participants tended to perform better at spatial and motor tasks, whereas female participants were on average superior at nonverbal reasoning and recognizing emotions. Moreover, the researchers also uncovered sex differences in resting-state functional brain connectivity. Unlike the earlier research, these differences were present at all ages, even in the youngest kids (which argues to some extent against a cultural or socialization account of the differences, though an easy rebuttal to this is that nine years is a fair amount of time for gender norms to sink in — testing even younger participants, or even sex-differences in animals, would help illuminate this issue). Perhaps most importantly, the researchers found a modest link between the two. The more stereotypically female vs. male a person’s brain, the more their cognitive profile was stereotypically female too, and vice versa.
“Taken together, these data provide novel evidence that the divergent patterns of cognition seen in males and females are reflected on a neural level in differential patterns of brain connectivity,” the researchers write. In other words, the scientists are arguing that at least part of the reason why the sexes have contrasting mental aptitudes is because of differences in their brain function — differences which are present from an early age.
Claims like this need to be handled very carefully because we live in an age where gender equality remains an aspiration rather than a reality. Women are grossly underrepresented in fields like science and senior management, and this situation is likely to be exacerbated by the suggestion that this may be because their brains are wired differently from men’s. For this reason it’s important to look very carefully at the fine print of the new study.
To investigate functional-connectivity patterns, the researchers looked at 264 functional “nodes,” or hubs (that is, places in the brain that are likely to support distinct mental activities), and at 36,716 specific functional connections (i.e. points of contact between two information channels). Just six of the nodes (2.3 percent) showed a difference between the sexes: Five exhibited signs of more within-node versus between-node connectivity in males compared with females; the other node exhibited more within-node connectivity in females than males. Regarding the thousands of connection points under study, just 0.51 percent showed a difference between the sexes. In short, the sex-based brain differences were miniscule. Towards the end of their paper, the researchers acknowledged this point: “While sex differences in connectivity exist,” they said, “on the whole connectivity patterns of male and female brains are more alike than different.”
Despite the subtlety of sex-based brain differences, the researchers still think they could help explain the cognitive-performance differences between males and females. For example, they suggested that the greater “network segregation” in female brains could allow for better performance in social cognition tasks on which women tend to average better performance than men. This is pure speculation, as the researchers themselves admit, and there’s no theory or evidence here to explain why or how the postulated neural differences would affect some mental functions and not others. Neuroskeptics will likely find more appeal in psychological explanations for the sex-based performance differences. For example, stereotype threat — a term for when our knowledge of stereotypes causes us to perform according to those stereotypes — is bound to play a powerful role. For example, one recent study found women matched men’s performance on math when they were taking part under a pseudonym, presumably because when their identity was concealed, they no longer felt the pressure to avoid fulfilling gender stereotypes about math skill.
On the other hand, the study of sex-based brain differences shouldn’t be swept under the carpet — for one thing, such research might help increase our understanding of why men and women differ in their vulnerability to different psychiatric and neurological disorders — men, for example, are much more often diagnosed with autism, while women are more vulnerable to the neuropathology associated with Alzheimer’s Disease. But the researchers’ late admission about the similarity of male and female neural connectivity reminded me of an extremely important point made by psychologist Cordelia Fine in Delusions of Gender, her book about “neurosexism” past and present. “The male brain,” she writes, “is like nothing in the world so much as a female brain.” These new results illustrate her point perfectly.
Dr. Christian Jarrett (@Psych_Writer), a Science of Us contributing writer, is editor of the British Psychological Society’s Research Digest blog. His latest book is Great Myths of the Brain.