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Battle of the brain’s sex differences…or not really?

Why some people are surprised at the very idea of there being differences between male and female brains I don’t understand. But, what really confuses me is when journalists misinterpret research findings and overextrapolate speculative comments to fit cliched gender stereotypes.

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“Brain networks show increased connectivity from front to back and within one hemisphere in males (upper) and left to right in females (lower).”
Credit: Ragini Verma, Ph.D., Proceedings of National Academy of Sciences, from press release.

Whenever I ask my (less sciencey) friends what they’d like to read on The Brain Bank, there is a perennially raised topic. At least one, usually single, hopeful will ask desperately for a guide on how men and women’s brains differ – and why they might work in different ways, scientifically speaking. Efforts to crack the mental codes of the opposite sex started as far back as Aristotle, who claimed that women were “more mischievous,  … more easily moved to tears[,] more apt to scold and to strike[,] … more void of shame or self-respect,…of more retentive memory” (History of Animals).

White matter tracts, as imaged using diffusion tensor imaging. Author: Xavier Gigandet et al., source here.

Earlier this month, a research paper from the University of Pennsylvania used a fancy imaging technique called diffusion tensor imaging (DTI) to solve the mystery behind the different ways guys and gals think. DTI basically gives you a picture of where the white matter tracts – the wiring between different brain areas – lie between various processing parts of the brain.

The technique works by looking at how water travels within the brain: water ‘prefers’ moving along bundles of fibres, such as white matter tracts. In this way, DTI examines the strength of ‘connectivity’ between various parts of the brain.

Researchers, led by Prof Ragini Verma, scanned the brains of 949 youths aged 8-22. They found that, in general, the connecting pathways within each half of the brain were stronger in guys, but that in girls, the wiring between the two halves was stronger. In other words, connectivity in girls tended to be more ‘left-right’, whereas in boys, ‘front-back’ connectivity was stronger.

The researchers also reported that the girls performed better on tests involving attention; word and face memory; and social cognition, whereas boys fared better on spatial processing and sensorimotor speed tasks.

NOT REALLY. Author: Miz Mura.

This paper and its associated press release rallied some…OK, a lot, of interest from the press. But then something strange happened. Something was lost in translation between the original paper and the resulting newspapers reports, claiming that ‘hardwired’ differences between men and women’s brains might explain ‘why men are better at map reading’ and women are more ‘emotionally intelligent’…

OH dear…

Seriously, NOT REALLY. Author: Miz Mura

…Then there was a knee-jerk reaction against the potentially neurosexist connotations of this ‘kind of science’, and not just because the research was published in PNAS (hehe). In my opinion, if a conclusion is based on valid and reliable science, you shouldn’t really argue unless you have definitely read the research. If, on the other hand, the offending ‘conclusions’ are the result of a bizarre ‘Chinese Whispers’ scenario where no one has actually read the original research, then no,  it’s probably not worth listening – but then, mistranslation isn’t based on science anyway…I digress.

While we all know that there are some obvious – and other more subtle – distinctions between men and women. This research article doesn’t actually claim to explain anything besides the physical connections between different parts of the brain. Just to clarify, here are some of the problems with treating this particular research paper as the Holy Grail of sex differences:-

1. There’s no saying whether there’s a big difference or not. The authors present (undeniably) a very striking diagram, with the statistically significant bits indicated in gender-relevant colours. However, just because a difference is statistically significant, doesn’t mean the effect of being male, or female is a big deal. In fact, as the study uses such a large sample (949 youths), even very small differences between male and female brains may prove significant.

2. Less wiring doesn’t necessarily mean lower ability. The authors don’t actually indicate anywhere in the paper that the ‘wiring’ is associated with men and women’s differing abilities on the tests – though Prof Verma has been quoted speculating on the possibility. Instead, the authors have pointed out the brain’s physical differences and then separately comment on behavioural differences without saying whether the two correlate.

If the hypothesis is that men or women with mega-strong connectivity left-to-right, or front-back are respectively better at, say, language, or football, you could easily find that out with a bunch of correlations. Not that correlation would imply causation anyway. In fact, the strengthening or weakening of physical connections could even suggest that women and men’s brains change to compensate for innate differences!

3. Size/proportions might matter. It’s pretty well-known that men have larger brains than women – the situation is pretty complicated though, as women reportedly have more grey matter, less white matter and a thicker cortex than men. However – please correct me if I’m wrong – the authors don’t correct for brain sizes (either front-back, left-right, total volume or any other measure), which could be very important. Especially considering the people being imaged are aged between 8 and 22, when brains grow a lot anyway. Not to mention that girls and boys grow at different rates too. Oh well.

Social media word clouds for females (top) and males (bottom). Size = strength of the correlation; color = relative frequency of usage. Underscores (_) connect words in phrases. Words and phrases in center; topics surround. Author: H. Andrew Schwartz et al.; Source. Apologies for the bad language!

4. There are many more potential mechanisms than meets the eye. Yes, it’s very possible that exposure to sex hormones could change the brain’s connectivity. But, there’s a whole host of other possible influences on a child going through puberty that can’t be ruled out, because the brain is notoriously/amazingly plastic. Environmental influences, influences that can’t ever be controlled for, such as parents, peers, teachers and the media – could just as easily alter the physical structures of the brain, or the brain’s abilities. In fact, hearing in the news that ‘men are better at map reading’ because it’s ‘hardwired’ in their brains is conceivably rather likely to make guys feel a bit more confident navigating, while discouraging women from taking that responsibility instead.

This piece of research is not the first and certainly won’t be the last to be accidentally misinterpreted or overhyped. Research into the differences between men and women will continue to fascinate us because, for whatever reasons – social, biological or otherwise – people of different sexes tend to look, sound and act differently. More seriously (and the authors of the paper explain the motivation of their research), sex differences are linked to brain disorders like autism and depression, so the differences between ‘Martians’ and ‘Venetians’ should be properly understood, and carefully reported.

For further examination of this topic, here’s another blog article and a BuzzFeed piece with a few more reasons why it should all be taken with a pinch of salt.

Post by Natasha Bray

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3 Responses to Battle of the brain’s sex differences…or not really?

  1. Pingback: Flashes of brilliance in the brain – the best Neuroscience images of 2013 | The Brain Bank

  2. Pingback: Tous mes voeux up’brain & up’spirit 2014 : flashes of brilliance in the brain – the best Neuroscience images of 2013 | Proâme

  3. Lise Eliot says:

    I wholeheartedly agree with your take. Please see my blog on the “sextrapolation” in this paper: http://www.huffingtonpost.com/lise-eliot/media-hype-and-the-scienc_b_4458458.html

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