This weekend, Big Think published a video to its YouTube channel featuring psychiatrist Gail Saltz claiming that conservatives and liberals have pronounced differences in “deeper brain structure(s).” According to Saltz, this difference is so pronounced that researchers can reliably predict whether someone is a liberal or a conservative simply by examining such structures.
So I think what’s really fascinating is that there have been a number of recent studies looking at brain structural differences between liberals and conservatives. And what’s been found in several studies is that liberals tend to have a larger anterior cingulate gyrus. That is an area that is responsible for taking in new information and that impact of the new information on decision making or choices. Conservatives tended on the whole to have a larger right amygdala. Amygdala being a deeper brain structure that processes more emotional information – specifically fear based information. So it’s really responsible for the flight or fright response. And this isn’t everybody. It’s not black and white and of course then, you know, what about all of the people in the middle? But basically the study showed that if you just based it on brain structural size different you could predict who would be a conservative and who would be a liberal with frequency of 71.6 percent.
Neither the video nor the transcript give any sources for this claim, but this appears to be based on a 2013 paper published in Plos One, Red Brain, Blue Brain: Evaluative Processes Differ in Democrats and Republicans. According to the abstract of the paper,
In particular, a recent study of young adults suggests that liberals and conservatives have significantly different brain structure, with liberals showing increased gray matter volume in the anterior cingulate cortex, and conservatives showing increased gray matter volume in the in the amygdala. Here, we explore differences in brain function in liberals and conservatives by matching publicly-available voter records to 82 subjects who performed a risk-taking task during functional imaging. Although the risk-taking behavior of Democrats (liberals) and Republicans (conservatives) did not differ, their brain activity did. Democrats showed significantly greater activity in the left insula, while Republicans showed significantly greater activity in the right amygdala. In fact, a two parameter model of partisanship based on amygdala and insula activations yields a better fitting model of partisanship than a well-established model based on parental socialization of party identification long thought to be one of the core findings of political science.
The problem here is that this study was widely–and justifiably in my opinion–criticized for its ridiculous methodology. Dan Kahan, Elizabeth K. Dollard Professor of law at Yale Law School, succinctly outlined the problems with the study in a post referring to the study as Deja voodoo.
Kahan outlines several problems, the most basic being that the study appears to be an exercise in data mining.
In an fMRI, brain activation (in the form of blood flow) is measured within brain regions identified by little three dimensional cubes known as “voxels.” There are literally hundreds of thousands of voxels in a fully imaged brain.
That means there are literally hundreds of thousands of potential “observations” in the brain of each study subject. Because there is constantly varying activation levels going on throughout the brain at all time, one can always find “statistically significant” correlations between stimuli and brain activation by chance.
. . .
Accordingly, if one is going to use an fMRI to test hypotheses about the “region” of the brain involved in some cognitive function, one has to specifyin advance the “region of interest” (ROI) in the brain that is relevant to the study hypotheses. What’s more, one has to carefully constrain one’s collection of observations even from within that region—brain regions like the “amygdala” and “anterior cingulate cortex” themselves contain lots of voxels that will vary in activation level—and refrain from “fishing around” within ROIs for “significant effects.”
Schreiber et al. didn’t discipline their evidence-gathering in this way.
What they did, instead, was make a prediction about how different regions of the brain would respond when exposed to risky stimuli. But their predictions turned out to be incorrect. But finding out the data contradict your hypothesis is just a minor speed bump.
But contrary to their hypotheses, Schreiber et al. didn’t find any significant differences in the activation levels within the portions of either the amygdala or the anterior cingulate cortex singled out in the 2011 Kanai et al. paper. Nor did Schreiber et al. find any such differences in a host of other precisely defined areas (the “entorhinal cortex,” “left insula,” or “Right Entorhinal”) that Kanai et al. identified as differeing structurally among Democrats and Republicans in ways that could suggest the hypothesized differences in cognition.
In response, Schreiber et al. simply widened the lens, as it were, of their observational camera to take in a wider expanse of the brain. “The analysis of the specific spheres [from Kanai et al.] did not appear statistically significant,” they explain,” so larger ROIs based on the anatomy were used next.”
Using this technique (which involves creating an “anatomical mask” of larger regions of the brain) to compensate for not finding significant results within more constrained ROI regions specified in advance amounts to a straightforward “fishing” expedition for “activated” voxels.
This is clearly, indisputably, undeniably not valid. Commenting on the inappropriateness of this technique, one commentator recently wrote that “this sounds like a remedial lesson in basic statistics but unfortunately it seems to be regularly forgotten by researchers in the field.”
Perhaps the video producers might want to re-brand to Small Think or No Think.