Brain Imaging Reveals a Neural Basis for Partisan Politics

Megan Brooks

October 27, 2020

The differences between politically left- and right-leaning individuals may have neural underpinnings, results from a new brain imaging study suggest.

Investigators found that despite watching the same videos related to immigration policy, neural responses differed between liberals and conservatives.

"This divergence was strongest when the videos used language that highlighted threat, morality, and emotions, suggesting that certain words are more likely to drive polarized response," lead researcher Yuan Chang Leong, PhD, a postdoctoral scholar in cognitive neuroscience at the University of California, Berkeley, told Medscape Medical News.

"The results suggest a neural basis for partisan biases in interpreting political messages, the effects these biases have on attitude change, and the type of language most likely to drive biased interpretations," Leong added.

The study was published online October 20 in Proceedings of the National Academy of Sciences.

Hardwired to Disagree?

The researchers combined fMRI with semantic content analysis to investigate neural mechanisms that underlie the biased processing of political content.

They scanned 38 middle-aged men and women with liberal- or conservative-leaning immigration attitudes while the participants watched short news clips, campaign ads, and public speeches related to various immigration policies.

These policies included those that led to the United States–Mexico border wall, Deferred Action for Childhood Arrivals (DACA) protections for undocumented immigrants, the ban on refugees from majority-Muslim countries coming to the United States, and the cutting of federal funding to sanctuary cities.

After each video, participants rated on a scale of 1 to 5 how much they agreed with the general message of the video, the credibility of the information presented, and the extent to which the video made them likely to change their position and to support the policy in question.

The study revealed evidence of "neural polarization" ― activity in the brain that diverges between people who hold liberal vs conservative political views, the researchers report.

Neural polarization was observed in the dorsomedial prefrontal cortex (DMPFC), a brain region associated with the interpretation of narrative content.

Neural polarization in this region intensified during moments in the videos that included risk-related and moral-emotional language, highlighting content features most likely to drive divergent interpretations between conservatives and liberals, they note.

For a given individual, the closer that brain activity resembled that of the "average conservative" or "average liberal," the more likely the person was to adopt that group's position after watching the videos.

"We know that partisans respond differently to the same information. So in that sense, it's not surprising to find that their brains respond differently as well," Leong told Medscape Medical News.

"What we weren't sure about was where in the brain we would find these differences, how neural differences were related to attitude change, and what type of content would be most likely to be associated with these differences," he said.

Importantly, said Leong, these differences do not imply that people are hardwired to disagree. Rather, individual experiences and the media that is consumed likely contribute to neural polarization.

"If our goal is to reduce polarization and change minds, we need to think carefully about how we frame and structure political information ― for example, by framing messages to appeal to the core values of the respective voter," he said.

Brain Stimulation to Alter Political Perception?

Reached for comment, Shaheen Lakhan, MD, PhD, neurologist in Newton, Massachusetts, and executive director, Global Neuroscience Initiative Foundation, said the research "puts us one step closer to identifying how our brains interpret political information."

The study, Lakhan noted, implicates a specific brain structure, the DMPFC, which is the "lens" in which information that gets into our brain is "viewed and acted on."

"I trust that there will be plenty more work using a similar fMRI approach to tease out scenarios outside of immigration policy, as used in this study. Down the line, brain signatures through fMRI may be able to tell an individual's political bent, and perhaps technologies like transcranial magnetic stimulation may be able to modulate our perceptions of political content, Shaheen said.

The research was supported by a grant from the Army Research Office. Leong and Lakhan have disclosed no relevant financial relationships.

Proc Natl Acad Sci. Published October 20, 2020. Abstract

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