By Tom Stafford, University of Sheffield
The Guardian: Male and female brains wired differently, scans reveal
The Atlantic: Male and female brains really are built differently
An analysis of 949 brain scans shows significant sex differences in the connections between different brain areas.
What they actually did
Researchers from Philadelphia took data from 949 brain scans and divided them into three age groups and by gender. They then analysed the connections between 95 separate divisions of each brain using a technique called Diffusion Tensor Imaging.
With this data they constructed "connectome" maps, which show the network of the strength of connection between those brain regions.
Statistical testing of this showed significant differences between these networks according to sex - the average men's network was more connected within each side of the brain, and the average women's network was better connected between the two hemispheres. These differences emerged most strongly after the age of 13 (so weren't as striking for the youngest group they tested).
How plausible is this?
Everybody knows that men are women have some biological differences - different sizes of brains and different hormones. It wouldn't be too surprising if there were some neurological differences too. The thing is, we also know that we treat men and women differently from the moment they're born, in almost all areas of life. Brains respond to the demands we make of them, and men and women have different demands placed on them.
Although a study of brain scans has an air of biological purity, it doesn't escape from the reality that the people having their brains scanned are the product of social and cultural forces as well as biological ones.
The research itself is a technical tour-de-force which really needs a specialist to properly critique. I am not that specialist. But a few things seem odd about it: they report finding significant differences between the sexes, but don't show the statistics that allow the reader to evaluate the size of any sex difference against other factors such as age or individual variability. This matters because you can have a statistically significant difference which isn't practically meaningful. Relative size of effect might be very important.
For example, a significant sex difference could be tiny compared to the differences between people of different ages, or compared to the normal differences between individuals. The question of age differences is also relevant because we know the brain continues to develop after the oldest age tested in the study (22 years).
Any sex difference could plausibly be due to difference in the time-course of development between men and women. But, in general, it isn't the technical details which I am equipped to critique. It's a fair assumption to believe what the researchers have found, so let's turn instead to how it is being interpreted.
One of the authors of this research, as reported in The Guardian, said "the greatest surprise was how much the findings supported old stereotypes". That, for me, should be a warning sign. Time and time again we find, as we see here, that highly technical and advanced neuroscience is used to support tired old generalisations.
Here, the research assumes the difference it seeks to prove. The data is analysed for sex differences with other categories receiving less or no attention (age, education, training and so on). From this biased lens on the data, a story about fundamental differences is also told. Part of our psychological make-up seems to be to want to assign essences to things - and differences between genders is a prime example of something people want to be true.
Even if we assume this research is reliable it doesn't tell us about actual psychological differences between men and women. The brain scan doesn't tell us about behaviour (and, indeed, most of us manage to behave in very similar ways despite large differences in brain structure and connectivity). Bizarrely, the authors seem also to want to use their analysis to support a myth about left brain vs right brain thinking. The "rational" left brain vs the intuitive' right brain is a distinction that even Michael Gazzaniga, one of the founding fathers of "split brain" studies doesn't believe any more.
When the headlines talk about "hardwiring" and "proof that men and women are different" we can see the role this research is playing in cementing an assumption that people have already made. In fact, the data is silent on how men and women's brains would be connected if society put different expectations on them.
Given the surprising ways in which brains do adapt to different experiences, it is completely plausible that even these significant "biological" differences could be due to cultural factors.
As Shakespeare has Ophelia say in Hamlet: "Lord, we know what we are, but know not what we may be."
The original paper: Sex differences in the structural connectome of the human brain
Sophie Scott of UCL has some technical queries about the research - one possibility is that movements made during the scanning could have been different between the sexes and generated the apparent differences in the resulting connectome networks.
Another large study, cited by this current paper, found no differences according to sex.
Cordelia Fine's book, Delusions of gender: how our minds, society, and neuro-sexism create difference provides essential context for looking at this kind of research. Fine has written a critique of this paper, for the Conversation UK's sister site in Australia.
Tom Stafford does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.