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Does (brain) size matter?

by on 2015/04/28

This week, the Telegraph reported on a study purporting to demonstrate that “Wealthier children have bigger brains”. In a surprise twist, the headline is not the most sensationalist part of the article, with the first sentence stating “Richer pupils achieve higher academic grades because their brains are different, according to research”. There is a fairly obvious overgeneralization on the direction of causality here (this type of study cannot distinguish whether bigger brains leads to higher grades brains or vice versa), but that’s a trap that the media routinely fall into.

The news article gives a broadly accurate overview of the study findings, noting that the income background of the pupils was related to increases in cortical thickness across their entire cortical surface. This finding is not, in itself, particularly novel – a well-publicised study last year showed similar effects in a very large cohort. The spin that the majority of the news coverage put on that earlier study was that poverty has a tangible effect on brain development, in contrast to the wealth-centric tone of the Telegraph article. The more novel aspect of the current study was showing that higher test scores in these same school pupils were also associated with increases in cortical thickness, but, critically, this relationship was confined only to the back half of the cortex. Put in this context, the statement at the top of the article seems like quite a leap – the general increase in cortical thickness associated with parental income is quite different from the very circumscribed set of regions which had thicknesses associated with higher test scores. Also, as pointed out by the authors of the research article (but sadly not mentioned in the media coverage), the relationship between cortical thickness and cognitive function is far from clear.

Interestingly, and not really touched upon in the news coverage, the parts of the brain which were thicker with increasing test scores (occipital regions – toward the back of the head, and temporal regions – around the ears) are not the parts of the brain which would be typically associated with the sort of cognitive function one would rely upon for test-taking (closer to your forehead – the prefrontal cortex). Instead, occipital regions are involved in all aspects of visual processing, whereas the temporal regions which show the association are involved in face processing and also in the processing of sounds. The article makes some mistakes here – it says this latter region is involved in storing knowledge – true in a strict sense, but only applicable to the part of the temporal lobe on the inside (medial) surface. No association between these memory areas was noted in any of the analyses in the paper.

As a final point of annoyance, the Telegraph article frequently refers to other work (“Past research has shown pupils from low-income backgrounds fared worse than those from wealthier families”), without including a link or citation. Indeed, it does not provide any link other than the Telegraph’s review of MIT. It does, however, pepper the space between the paragraphs in the article with links to other not-ostensibly relevant studies (“Men really are more stupid than women, research shows” – one that I’m pretty disappointed that we missed last year…).

Mackey A.P. et al. (2015). Neuroanatomical Correlates of the Income-Achievement Gap. Psychological Science. DOI:10.1177/0956797615572233

Noble K.G. et al. (2015). Family income, parental education and brain structure in children and adolescents. Nature Neuroscience. DOI:10.1038/nn.3983

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