People with even slightly different political views process information using different patterns of brain activity. A recent brain imaging experiment reveals that listening to political statements about immigration prompts synchronized neural responses among individuals who share similar attitudes. These findings, published in iScience, suggest that the biological roots of political division extend to subtle ideological disagreements.
In recent years, researchers have documented a biological phenomenon called neural polarization. This occurs when the brain activity of individuals holding similar political beliefs synchronizes while they consume political content. At the same time, their brain activity diverges from people who hold opposing views. Past studies typically focused on stark divides in the United States or Israel, comparing staunch conservatives to strong liberals.
These previous experiments often found that political attitudes influence how the brain processes information. Some research pointed to polarization in higher-order brain regions responsible for complex thought. Other studies found that political leanings alter activity in lower-order areas responsible for basic sensory perception.
A team of researchers wanted to know if this biological divide happens even among people whose political views are only slightly different. The research was led by neuroscientists Niloufar Zebarjadi and Annika Kluge at Aalto University in Finland, along with Jonathan Levy at Bar-Ilan University in Israel. They designed an experiment focusing on attitudes toward immigration in Finland.
Finland has a multiparty political system with relatively low levels of societal polarization compared to other Western nations. Because the country is not strictly divided into a two-party system, it provides an ideal setting to study subtle ideological differences. The researchers wanted to see if identical information is interpreted differently depending on minor variations in a person’s worldview.
The researchers recorded fMRI data from 48 participants, of whom 40 remained after exclusions and were included in the final analysis. Functional magnetic resonance imaging, or fMRI, tracks blood flow in the brain to measure neural activity in real time. While inside the scanner, the participants listened to 44 audio statements about immigration to Finland.
Half of these statements supported immigration, and the other half opposed it. The audio clips were specifically balanced to ensure they were similar in length and grammatical structure. Some statements focused on immigration in general, while others specifically mentioned Muslim immigrants.
After hearing each statement, participants rated how much they agreed with the message on a five-point scale. The researchers used these ratings to calculate an overall immigration attitude score for each person. After the scanning session, participants also filled out several questionnaires measuring their political inclination, empathy, and attitudes toward multiculturalism.
The participants’ immigration attitude scores strongly correlated with their survey answers. Those who scored lower on immigration support also reported higher levels of perceived threat and discriminatory attitudes. The researchers divided the participants into two groups of 20 based on a median split of their immigration attitude scores. Both groups were generally supportive of immigration, but one group was highly supportive while the other was slightly less supportive.
To find evidence of neural polarization, the researchers used a technique called inter-subject correlation. This method looks at how the activity in tiny sections of the brain rises and falls over time. The researchers compared the brain activity time courses among people in the same group and compared them against people in the opposing group.
If the brain waves in a specific area synced up closely among people in the same group, but did not sync up with the other group, that area was marked as polarized. When analyzing all the audio statements together, the researchers found that brain activity was more similar among people in the same group than it was between the two groups. This divergence appeared in two specific brain areas: the left dorsolateral prefrontal cortex and the left premotor cortex.
The dorsolateral prefrontal cortex is a region associated with complex cognitive tasks like reasoning, memory, and decision making. The premotor cortex is traditionally involved in planning physical movements. Finding differences in both areas indicates that political attitudes filter information through high-level thinking centers as well as lower-level regions tied to physical action.
Next, the researchers analyzed the data to see if the type of political narrative changed the brain’s response. They separated the brain scans recorded during the pro-immigration audio from the scans recorded during the anti-immigration audio. They repeated their inter-subject correlation analysis for each set of data.
When participants listened to pro-immigration statements, the researchers observed a similar pattern of neural polarization. The brain activity diverged between the highly supportive and less supportive groups in the left dorsolateral prefrontal cortex and the right premotor cortex. The results closely mirrored the findings from the overall analysis.
When participants listened to anti-immigration statements, the brain mapping looked different. Neural polarization still appeared in the dorsolateral prefrontal cortex, though in the right hemisphere instead of the left. The researchers also found polarized activity in the primary somatosensory cortex, which processes physical sensations like touch.
Another area that showed polarization during anti-immigration audio was the superior temporal gyrus. This part of the brain is involved in processing sounds and understanding language. By comparing the overall level of synchronization, the researchers noticed another pattern during the anti-immigration narratives.
The group that was less supportive of immigration showed a stronger degree of neural polarization than the highly supportive group. The brain responses were distinctly sensitive to the political leaning of the audio content. The researchers noted that focusing on specific polarizing topics, such as immigration, can alter how different ideological groups biologically process political speech.
There are several limitations to consider when interpreting these results. The study group consisted mostly of individuals who favored immigration, and a majority identified as politically left-leaning. Because the participants were mostly uniform in their overall support for immigration, the findings might look different in a highly divided population with extreme opposing views.
The study relied on an observational design, meaning it cannot prove that a person’s political beliefs caused their brain activity to change. It is possible that underlying biological differences influence a person’s political attitudes. The self-reported nature of the surveys also means that some participants might not have revealed their true attitudes due to social pressures.
The participant pool was relatively small, heavily female, and drawn from a single industrialized, democratic country. The researchers also pointed out that the findings were not statistically significant when the groups were analyzed completely separately for some of the brain regions, likely due to reduced statistical power from dividing a small sample size. Expanding the research to include larger, more diverse groups of people would help determine how universal these patterns of neural polarization might be.
Scientists are continuing to investigate how biological mechanisms relate to political beliefs. The study, “Polarized neural responses to political narratives are sensitive to small variations in self-reported political perspectives,” was authored by Niloufar Zebarjadi, Annika Kluge, Enrico Glerean, Matilde Tassinari, Iiro P. Jääskeläinen, Inga Jasinskaja-Lahti, and Jonathan Levy.