Political Views Bias Information Processing in the Brain

Post by Deborah Joye

What's the science?

With an important election fast approaching in the United States, it is clearer than ever that political polarization exists in our society. A powerful contributor to political polarization is motivated reasoning; when we make decisions based on emotional bias rather than evidence or facts. Motivated reasoning is made especially obvious when people with opposing beliefs are presented with identical information and their biased interpretation leads them to become even more entrenched in their original positions.

But how might identical information trigger such different outcomes, and can we see these different responses in the brain? It’s possible that our previously held beliefs change what we pay attention to when we absorb new information. For example, someone might view a political ad and only pay attention to information that supports their beliefs. It’s also possible that previously held beliefs change how people interpret incoming information. For example, one person may interpret actions as threatening, risky, or offensive where someone with different beliefs might not. This week in PNAS, Leong and colleagues demonstrate that when viewing political content,  conservative- and liberal-leaning people displayed differential activation of the dorsomedial prefrontal cortex which was intensified by moral-emotional and risk-related language.

How did they do it?

The authors scanned thirty-eight participants with functional magnetic resonance imaging (fMRI) while they viewed videos on immigration policies. Before scanning, participants indicated their support for each of the policies, and the authors calculated an overall “Immigration Attitude” to identify liberal- and conservative-leaning participants. Importantly, the authors controlled for age, sex, income, and education. The authors first asked if neural responses to the videos were different across participants. They calculated an intersubject correlation; a measure of how similar brain activity is across participants. This measure also allowed the authors to investigate which regions of the brain exhibited differential activity..

The authors next asked whether differential brain activity was specifically associated with certain content within the videos. The authors categorized words in the videos that were related only to emotions (e.g. fear, sad, etc.), related only to morals (e.g. ethics, etc.), or related to both morals and emotions (e.g. compassion, harm, etc.). The authors identified a total of 50 categories, including risk, religion, power, family, social, male, and female, among others. Finally, the authors asked whether brain activity that was more like either political group might predict the participant’s preference for supporting the position held by that group. To assess this, the authors averaged brain activity across both groups, creating a map of what the signal might look like for an “average” liberal or conservative. After each video, the authors asked each participant whether they’d be more or less likely to support that policy. The authors then assessed whether a particular participant’s brain activity during that video was more like that of the average conservative or the average liberal.

What did they find?

The authors found that overall neural responses to the political videos were shared across participants. Specifically, regions of the brain related to sensory processing displayed similar activity patterns regardless of the participant’s political leanings, suggesting that political attitudes do not alter sensory processing. However, activity patterns in the dorsomedial prefrontal cortex diverged between liberal and conservative participants. Previous research has demonstrated that this brain region is known to be active when participants are manipulated to have different interpretations of an ambiguous story. 

The authors also found that the difference in activity patterns in the dorsomedial prefrontal cortex was associated with the use of moral-emotional and risk-related language, suggesting that those categories of language are most likely to drive divergent neural responses between liberals and conservatives. The authors also found that connectivity between the ventral striatum (associated with emotional processing) and the dorsomedial prefrontal cortex was more similar for participants with similar political views. Lastly, the authors found that for each video, whether a participant’s neural activity was more like the average conservative or liberal predicted their attitude change. For example, a participant with brain activity patterns more like the average conservative was more likely to display attitude change further in the conservative direction.

What's the impact?

This study found that political attitudes can drive divergent neural processing of political information. One striking implication of these findings has to do with the “echo chamber” of social media, where online videos with moral-emotional content tend to spread faster within social circles sharing similar political beliefs. These findings suggest people with already formed political biases will respond to such political content with further attitude polarization. This study also demonstrates that content that features moral-emotional and risk-related language is most likely to be processed in this biased way. These findings have important implications for our political discourse moving forward and have implications for the type of language we use in a political context, as well as the impact this may have on an increasingly polarized society.

Leong et al., Conservative and liberal attitudes drive polarized neural responses to political content, PNAS (2020). Access the original scientific publication here.