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Gender-specific findings of new brain-connectivity study are questioned

connectome map
Researchers created “connectome” maps for 428 males and 521 females aged 8 to 22 years.

A press release about a new brain connectivity study published earlier this week in the Proceedings of the National Academy of Sciences (PNAS) declared that the study had found “striking differences” in the neural wiring of men and women.

The release — and many media headlines that followed — also stated that this finding might help explain some commonly held beliefs about cognitive gender differences, including the ones about how men are better at map reading and women are better at remembering names and faces.

In fact, one of the authors of the study told a reporter for the Guardian newspaper that “the greatest surprise was how much the findings supported old stereotypes.”

But wait a minute. Do the findings from the study actually support such gender stereotypes? Or, as one academic psychologist charges, is this another case study in neurosexism?

An analysis of ‘connectomes’

First, some details about the study itself: A team of researchers from the University of Pennsylvania used a technology called diffusion tensor imaging (DTI) to trace how brain cells are connected (the neural circuitry) between 95 separate regions of the brain. Nearly 1,000 people — 428 males and 521 females aged 8 to 22 years — underwent the imaging.

Armed with a “connectome” map for each participant’s brain, the researchers did some statistical analysis and found that female brains, on average, exhibited greater connectivity between the left and right hemispheres and within the cerebrum, the largest part of the brain.

Males, on the other hand, showed greater neural connectivity within each hemisphere of the brain.

Interestingly, the differences between the genders became significant only in the participants aged 13 and older.

Based on these findings, the study’s authors concluded in their paper that “male brains are structured to facilitate connectivity between perception and coordinated action, whereas female brains are designed to facilitate communication between analytical and intuitive processing modes.”

One of the authors, Ragini Verma, an associate professor of radiology at PENN, put it this way to a reporter for the Guardian newspaper: “If you look at functional studies, the left of the brain is more for logical thinking, the right of the brain is for more intuitive thinking. So if there’s a task that involves doing both of those things, it would seem that women are hardwired to do those better. Women are better at intuitive thinking. Women are better at remembering things. When you talk, women are more emotionally involved — they will listen more.”

She then seemed to suggest that the findings explain why men make better chefs and hairstylists.

Head motion and brain size

That’s a big leap to make from this study’s findings, as quite a few other researchers quickly made clear. For the study had several problematic limitations. First, there’s the issue of brain motion.

“A paper just last week showed convincingly that even modest amount of head motion during the MRI scan causes changes in DTI,” writes “Neuroskeptic,” a well-respected (and anonymous) research psychologist who blogs for Discover magazine.

“It’s not implausible,” Neuroskeptic explains, “that men and women might move different amounts on average, so that may account for at least some of these results.”

Then there’s the issue of brain size. On average, men tend to have bigger brains than women, a factor that might affect DTI estimates of connectivity. As Neuroskeptic points out, “Longer connections — as seen in bigger brains — are weaker (or at any rate, appear weaker on DTI).”

A possible cultural explanation

But there are other warning signs about the study and its findings. Here’s one posed by University of Sheffield psychologist and researcher Tom Stafford on his Mind Hacks blog (with British spellings):

Time and time again we find, as we see here, that highly technical and advanced neuroscience is used to support tired old generalizations.

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 anymore.

Perhaps more importantly, analysis of how men and women are doesn’t tell you how men and women could be if brought up differently. … 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.

‘Trivially small’ differences

Cordelia Fine, a psychologist at the University of Melbourne and the author of “Delusions of Gender: How Our Minds, Society, and Neurosexism Create Difference,” agrees with Stafford. She also points out another problem with the study’s findings:

[P]opular references to women’s brains being designed for social skills and remembering conversations, or male brains for map reading, are utterly misleading.

In an larger earlier study (from which the participants of the PNAS study were a subset), the same research team compellingly demonstrated that the sex differences in the psychological skills they measured — executive control, memory, reasoning, spatial processing, sensorimotor skills, and social cognition — are almost all trivially small.

To give a sense of the huge overlap in behaviour between males and females, of the twenty-six possible comparisons, eleven sex differences were either non-existent, or so small that if you were to select a boy and girl at random and compare their scores on a task, the “right” sex would be superior less than 53% of the time.

Even the much-vaunted female advantage in social cognition, and male advantage in spatial processing, was so modest that a randomly chosen boy would outscore a randomly chosen girl on social cognition — and the girl would outscore the boy on spatial processing — over 40% of the time.

As for map-reading and remembering conversations, these weren’t measured at all.

Yet the authors describe these differences as “pronounced” and as reflecting “behavioural complementarity” — scientific jargon-speak for “men are from Mars, women are from Venus.” Rather than drawing on their impressively rich data-set to empirically test questions about how brain connectivity characteristics relate to behaviour, the authors instead offer untested stereotype-based speculation. Even though, with such considerable overlap in male/female distributions, biological sex is a dismal guide to psychological ability.

The PNAS study, she concludes, is the “latest case study in how easily scientific ‘neurosexism’ can, with a little stereotype-inspired imagination, contribute to inaccurate and harmful lay misunderstanding of what neuroscience tells us about the sexes.”

You’ll find the study at the PNAS website. The analyses of the study by Neuroskeptic, Stafford and Fine can be found at the links above.

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Comments (1)

  1. Submitted by Paul Brandon on 12/05/2013 - 12:15 pm.

    The key point here

    is the degree of overlap between the male and female populations in the studies. While the -population- differences may be statistically significant, if the male and female populations show a large overlap (as appears to be the case) the data is useless as a predictor of -individual- behavior.

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