The way your brain reacts to a single disgusting image can be used to predict whether you lean to the left or the right politically.
A number of studies have probed the emotions of people along the political spectrum, and found that disgust in particular is tightly linked to political orientation. People who are highly sensitive to disgusting images – of bodily waste, gore or animal remains – are more likely to sit on the political right and show concern for what they see as bodily and spiritual purity, so tend to oppose abortion and gay marriage, for example.
A team led by Read Montague, a neuroscientist at Virginia Tech in Roanoke, recruited 83 volunteers and performed fMRI brain scans on them as they looked at a series of 80 images that were either pleasant, disgusting, threatening or neutral. Participants then rated the images for their emotional impact and completed a series of questionnaires that assessed whether they were liberal, moderate or conservative.
The brain-imaging results were then fed to a learning algorithm which compared the whole-brain responses of liberals and conservatives when looking at disgusting images versus neutral ones.
For both political groups, the algorithm was able to pick out distinct patterns of brain activity triggered by the disgusting images. And even though liberals and conservatives consciously reported similar emotional reactions to the images, the specific brain regions involved and their patterns of activation differed consistently between the two groups – so much so that they represented a neural signature of political leaning, the team concludes.
Conservatives showed increased activity in brain regions previously implicated in processing disgust, such as the basal ganglia and amygdala, but also in a wide range of regions involved in regulating emotion, attention and integrating information. In liberals the brain showed increased activity in different regions, but these were just as diverse.
The team found that these neural signatures of disgust can be used to predict political orientation. “In fact, the responses in the brain are so strong that we can predict with 95 per cent accuracy where you’ll fall on the liberal-conservative spectrum by showing you just one picture,” says Montague. “This was surprising as there are no other reports where people’s response to just one stimulus predicts anything behaviourally interesting.”
Darren Schreiber of the University of Exeter, UK, who is also interested in the neuroscience of politics, says this approach is an advance on previous brain-imaging work that highlighted the importance of one or two isolated brain regions on political leaning, rather than entire networks.
And while this is not the first time differences have been found in the brains of liberals and conservatives, Schreiber says that the combination of whole-brain analysis with a sophisticated learning algorithm marks a step forward. “It’s not only a powerful replication and extension of previous work, but it’s also incredibly accurate.”
Journal reference: Current Biology, DOI: 10.1016/j.cub.2014.09.050