Wednesday, December 03, 2014

What's For Breakfast? Different Size Brains. Today's Gender Research Which Didn't Attract Attention.

The title of this post (about breakfast) refers to a study which came out exactly a year ago, the one which argued that girl brainz and boy brainz are wired utterly different.  Remember it?  I read it while having breakfast and it's eternally associated in my girl brain with hash and fried eggs.

 Here's my summary of the earlier study.  This post reads a lot better if you read the earlier one first.  It's also a funny post, so you might not regret the minutes you spend there.

That study by Ingalhalikar et al. argued that men and women have fundamentally different patterns of brain organization.  The researchers then put on their skates to skate on thin ice about how these differences are linked to the ways brains are used.  In particular, they argued that women have brains built for social cognition and better memory and that men have brains built for clear perception-action patterns and for better motor skills.

Then the floodgates opened in the popularizations of the study (and it sure was popularized) as well as in the many, many comments attached to those popularizations (yeay! gender essentialism rules!).

But the researchers themselves didn't help much.  For instance, one of the researchers in the study, Ragini Verma, suggested in interviews that the study might support the idea that men are better map-readers and that women might be better multi-taskers or emotional listeners.

This despite the fact that although the study did try to link the imaging studies to sets of questionnaires about cognition those questions didn't include map-reading at all, for instance.

The footnote to my earlier post noted a few more technical criticisms of the study.  One is an alternative hypothesis about the way brains are organized.  Cornelia Fine sums it like this:

One important possibility the authors don’t consider is that their results have more to do with brain size than brain sex. Male brains are, on average, larger than females and a large brain is not simply a smaller brain scaled up.
Larger brains create different sorts of engineering problems and so – to minimise energy demands, wiring costs, and communication times – there may physical reasons for different arrangements in differently sized brains. The results may reflect the different wiring solutions of larger versus smaller brains, rather than sex differences per se.

Now a new study has addressed that hypothesis (thanks to DB for the link).  Here's the abstract:

Twenty years ago, Ringo and colleagues proposed that maintaining absolute connectivity in larger compared with smaller brains is computationally inefficient due to increased conduction delays in transcallosal information transfer and expensive with respect to the brain mass needed to establish these additional connections. Therefore, they postulated that larger brains are relatively stronger connected intrahemispherically and smaller brains interhemispherically, resulting in stronger functional lateralization in larger brains. We investigated neuronal interconnections in 138 large and small human brains using diffusion tensor imaging-based fiber tractography. We found a significant interaction between brain size and the type of connectivity. Structural intrahemispheric connectivity is stronger in larger brains, whereas interhemispheric connectivity is only marginally increased in larger compared with smaller brains. Although brain size and gender are confounded, this effect is gender-independent. Additionally, the ratio of interhemispheric to intrahemispheric connectivity correlates inversely with brain size. The hypothesis of neuronal interconnectivity as a function of brain size might account for shorter and more symmetrical interhemispheric transfer times in women and for empirical evidence that visual and auditory processing are stronger lateralized in men. The hypothesis additionally shows that differences in interhemispheric and intrahemispheric connectivity are driven by brain size and not by gender, a finding contradicting a recently published study. Our findings are also compatible with the idea that the more asymmetric a region is, the smaller the density of interhemispheric connections, but the larger the density of intrahemispheric connections. The hypothesis represents an organization principle of the human connectome that might be applied also to non-human animals as suggested by our cross-species comparison.

Bolds are mine. To re-hash (a pun on the breakfast title):  The effect the researchers found between larger brains and smaller brains was independent of gender*, even though it's true that women, on average, have smaller brains than men, on average.  This gives tentative support to the idea that the patterns Ingalhalikar et al. found has more to do with organizational efficiency in different sized brains than with the ways the brains are used etc.

I have read this new study but not for the purpose of critiquing it.  The minute it is splashed across the front pages of the Guardian and all those other newspapers, the same way the Ingalhalikar et al. study was, I will spend the necessary time on such a critique (heh).  But the important take-home points are two:  The earlier study did not control for the size of the brain and the study which looked at that did not get publicized like the second coming of Echidne.

*As the study states:
There is a highly significant interaction between brain size (small vs. large brains) and the type of connectivity (interhemispheric vs. intrahemispheric connectivity) across the whole sample. The same interactions can be found when comparing small vs. large female brains and small vs. large male brains.