Showing people pictures of roadkill or fresh vomit might not win you any points at your next dinner party, but it will at least give you a window into their psyches. A new study finds the same mechanisms that determine feelings of revulsion can reliably predict people’s political affiliations.

The neuroscience of political ideology is relatively new. It’s emerged within the last decade, as scientists begin to learn the simple act of casting a vote actually predicts a wide range of other preferences, behaviors, and beliefs. If the proxy is strong enough, it could allow future researchers to investigate the inner workings of one or two brain regions, as opposed to the time-consuming job of probing entire neural networks.

"The responses in the brain are so strong that we can predict with 95-percent accuracy where you'll fall on the liberal-conservative spectrum by showing you just one picture," said Read Montague, lead author and neuroscientist at Virginia Tech University, in Roanoke. The effect was especially surprising, he added, because no other study has found a response to just one stimulus that "predicts anything behaviorally interesting."

To understand how political leaning may manifest itself in other behavioral responses, the researchers recruited 83 volunteers to lie inside an fMRI scanner and view a series of 80 images. These images were either pleasant, disgusting, threatening, or neutral. Subjects rated their reactions toward each one, then filled out a several questionnaire designed to judge whether they were liberal, moderate, or conservative.

When the fMRI scans were fed into a machine that analyzes patterns in the brain, which the team based on the follow-up political questionnaires, distinct patterns emerged. They weren’t just vague similarities, though. The findings were so robust that the team referred to the patterns as neural signatures — precise impressions that seemed to reflect key underlying structures in the brain.

One Changes The Other

The findings aren’t the first look into the neurological makeup of political ideology. In 2012, for instance, scientists from the University of California, Santa Barbara, found a clear correlation between the sizes of certain brain regions and people’s moral viewpoints. How they responded to statements like “People should not do things that are disgusting, even if no one is harmed” and “I think it’s morally wrong that rich children inherit a lot of money while poor children inherit nothing” later showed up in brain scans as either larger or smaller prefrontal cortexes, which guide basic behavior. People who scored highly on the team’s “purity index” also had more voluminous anterior insula, which is strongly related to disgust.

The same findings have been replicated in several studies using the Implicit Association Test (IAT), which exploits people’s kneejerk reactions to certain pairings to determine their latent racism, sexism, ageism, and other such biases. According to the IAT, a person who spends a fraction of a second more looking at a black person paired with the word “scary,” over some other more positive or neutral word, carries more of a bias. These biases can only be measured at the unconscious level, the test argues.

But of course ideology and feelings of disgust aren’t always so deep-seated. Neuroscience knows the brain is relatively plastic. If a person grows up in a conservative home but attends a liberal college, his neural signature is likely to change as the ideas he’s exposed to shift from red to blue.

More profound, the neuroscience today suggests the behavior will change, too. In shifting political affiliations, past sentiments about what it means to be “pure” or “sacred” lose their meaning to new definitions. And what once seemed disgusting is now surprisingly palatable. This bodes well for neuroscientists looking to understand how the brain responds to stimuli, both in the short- and long-term.

To the Virginia Tech researchers, the new study adds a finer point to the general findings of the past. "It's not only a powerful replication and extension of previous work,” said Darren Schreiber, of the University of Exeter, in the UK, to NewScientist. “But it's also incredibly accurate."

Source: Ahn W, Kishida K, Gu X, et al. Nonpolitical Images Evoke Neural Predictors of Political Ideology. Current Biology. 2014.