Why Bigger Isn’t Always Better

One of my entertainments this holiday season was following the online buzz over a recent article in Nature Neuroscience. The authors’ findings were covered by Wired, Time, Slate, U.S. News & World Report, and the BBC, to name a few. One headline read: Scientists Discover Facebook Center of the Brain. Another: How to Win Friends: Have a Big Amygdala?

The authors of the Nature Neuroscience article report a correlation between the size of a subcortical brain structure called the amygdala and the extent of a person’s social network. In effect, people with larger amygdalas tended to have more friends and close acquaintances than those with lesser-sized amygdalas. The popular press and the public leapt on this idea. We are predestined by our anatomy to be popular or not. If we were alone on New Years Eve, if our Facebook friend count is low, it’s not our fault. Chalk that one off to our brains, our genes, our parents.

All of this struck me as both amusing and sad because of a book I was reading at the time. The book, Postcards from the Brain Museum by Brian Burrell, chronicles the history of neuroscience in the context of our search for greatness (as well as criminality, idiocy, and inferiority.) It tells how scientists spent most of the 19th century collecting human brains from geniuses, criminals, and the poor to try to understand why some people demonstrate remarkable abilities while others flounder and fail.

It is a sad and sordid history. At first, some believed that the sheer size or weight of one’s brain predicted greatness, so that large brains were capable of better thinking. Since women’s brains (like the rest of their bodies) were on average smaller than those of their male counterparts, this provided a perfect explanation for their intellectual inferiority. Later, when the link between brain volume and intelligence was debunked, scientists suggested that the amount of folding on the brain’s surface was the marker of a brilliant brain. The more convolutions on the surface, the smarter the individual. Other scientists identified specific fissures that they deemed inferior, as they were supposedly found more often in apes and women. These lines of research would be used to justify racial and gender stereotypes and give rise to the practice of eugenics in the first half of the 20th century.

The peer review process and established statistical methods ensure that today’s science is more legitimate than it was in centuries past. But neuroimaging has allowed us to probe the living brain to a degree heretofore unimagined. With it, scientists amass enormous amounts of data that strain our standard statistical techniques and challenge our ability to distinguish between profound, universal discoveries and those idiosyncratic to our subject sample or functionally irrelevant. We still don’t know whether ‘bigger is better’ nor understand the source or functional consequences of individual differences in the size and shape of brain regions. Certainly we don’t know enough to look at a person’s brain and guess with accuracy how smart they are, how good they are, or, yes, even how many friends they have.

Just look at this graph from the Nature Neuroscience paper plotting amygdala volume on the horizontal axis and social network size on the vertical axis:

The figure above shows each subject as a black dot (for younger participants) or a gray triangle (for older ones). The diagonal line shows a mathematical correlation between amygdala volume and social network size, but look at how many dots and triangles lie away from the line. For the same amygdala volume (say, 3 cubic mm), there are dots that lie far above the line and others that lie far below it. No one looking at this figure can say that amygdala size determines one’s sociability. Perhaps it plays some small role, sure. But we are not slaves to our amygdala volumes, just like we’re not slaves to our overall brain size, our fissural patterns or cerebral convolutions. Our abilities and thoughts do come from our brains, but we have to keep in mind that those brains are far more complex than we can fathom. Who you are can never be reduced to a list of measured volumes. It’s important that we remember that, and that we never return to those days of ‘mine’s bigger than yours.’

One response

  1. thanks for writing this post. i just presented that paper at my department’s journal club, and i was surprised that nobody actually made this point. the correlations are not very strong, and even still, what exactly brain volume has to do with social stuff is not totally clear and certainly not from this article.

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