Does brain size matter: time to stop this nonsense

It’s male and female brains time again! Why are some researchers and journalists hooked on sensationalism? Our resident neurotrash warrior Prof Gina Rippon takes a look behind the headlines at the latest offender. She’s not going anywhere – and we’re not standing for this nonsense any longer. We want better science.

Gina  will be tackling all sorts of gender-based neurotrash to celebrate International Women’s Day on 8th March 2014. Come and meet her at the Southbank Centre at our partner session with the WOW Festival.

Prof Gina Rippon

Prof Gina Rippon

Meta-study gets dramatic headlines

So…. here we go yet again!! “Men really DO have bigger brains” – that was the Daily Mail’s take on a newly published study by Ruigrok et al  from Simon Baron-Cohen’s Cambridge group. A meta-analysis of an number of studies on structural differences in brains from men and brains from women has shown group differences in certain brain regions; more specifically that men on average have larger volumes and/or higher tissue densities in some structures (e.g. left amygdala, some hippocampal areas) and women on average have larger volumes and/or higher tissue densities in other structures (e.g. left frontal pole).

Important aspects such as body size largely ignored

A key aspect in these studies is that these are absolute volumes – i.e.  not corrected for body size, weight and height. It’s true that the authors point this out by blaming “conventional” ways of reporting such data – but by not challenging it they are now themselves, of course, contributing to such murky literature. This is no minor failing: various studies explicitly state such considerations are absolutely central to how you interpret apparent or alleged differences in brain structures. For example:

  • Leonard et al (2008): Size matters: cerebral volume influences sex differences in neuroanatomy.
  • Barnes et al (2010) Head size, age and gender adjustment in MRI studies: a necessary nuisance?

The team also acknowledge that other “important sources of statistical noise” (e.g. differences in analysis, sample size – the list goes on) could have significantly influenced their findings. This leaves me wondering why this was not, apparently, sufficiently important to give the authors pause for thought as to the advisability of carrying out such comparisons in the first place. This huge caveat was, completely predictably, not picked up by populist reporting.

Brains are plastic not hard-wired

We are given details as to the sex and age of the participants in these studies – but this is nowhere near enough information. Apart from the fact that dividing individuals purely into ‘male’ and ‘female’ is overly simplistic, it plays into the idea that our brains are ‘hard-wired’ and there’s nothing we can do about it. In fact, we know that our brains are exquisitely plastic throughout our lifetime, and our socio-economic status, our learning experiences, health, exposure to toxins, in fact, eating, drinking and being merry (or learning to juggle or tango) can change our brains, see Fine et al (2013).I covered this in more detail in my previous post here.

Does brain size affect how it works?

Which brings me to the next problem. Does knowing what a brain looks like mean we know how it works? No. Has it been proved that having a bigger/smaller amygdala/ hippocampus will result in the kind of behavioural dysfunctions that get you labelled as autistic or schizophrenic? No, it hasn’t.

We do know that to understand human behaviour we need to understand networks of activity in the brain, different areas being briefly coupled and uncoupled in events measured in milliseconds. Huge amounts of money in the US and in Europe are being poured into projects to understand the ‘Human Connectome’. That is where the focus should be, not on yet another contribution to the ‘Size Matters’ agenda.


So, behind the headlines, what we have here is a paper reporting group average differences in some structures in brains where there has been no allowance for differences in size, height and weight of their owners. A paper which explicitly states that (in the text but not in the abstract) that “no predictions as to how structure may influence physiology or behaviour are possible from these meta-analyses”.

I believe these authors are overstating the value of their observations which, alone, is problematic. A meta-analysis is only as good as the studies it covers, and although this one was detailed and on an impressive number of studies, in this case I think many wrongs don’t add up to a right. And when findings such as these are so open to misreporting and misrepresentation, researchers in this field should really think things through more carefully before hitting the ‘Submit’ button.

Fine, C., Jordan-Young, R., Kaiser, A., & Rippon, G. (2013). Plasticity, plasticity, plasticity… and the rigid problem of sex. Trends in cognitive sciences, 17 (11), 550-551
Leonard, CM et al (2008): Size matters: cerebral volume influences sex differences in neuroanatomy. Cerebral Cortex, 18 (12) 2920-2931
McCarthy, M. M., & Arnold, A. P. (2011). Reframing sexual differentiation of the brain. Nature Neuroscience, 14(6), 677-683
Ruigrok et al (2014) A meta-analysis of sex differences in human brain structure.  Neuroscience & Biobehavioural Reviews (in press)