Study suggests political ideology is associated with differences in brain structure, but less than previously thought

Conservative voters have slightly larger tonsils than progressive voters, about the size of a sesame seed. In a replication study published Sept. 19 in the journal iScience, The researchers revisited the idea that progressive and conservative voters have identifiable differences in brain morphology, but with a sample 10 times larger and more diverse than the original study.

Their results confirmed that the size of a person’s amygdala is associated with their political views, but failed to find a consistent association between politics and the anterior cingulate cortex (ACC).

Anatomical differences in the amygdala and ACC vary depending on a person’s economic and social ideology (which are not necessarily aligned), indicating that the relationships between political ideology and brain structure are nuanced and multidimensional.

“It was really a surprise to see that we replicated the results we got in the amygdala,” says Diamantis Petropoulos Petalas, first author and researcher in political psychology and neuroscience at the American College of Greece and member of the @HotPoliticsLab at the University of Amsterdam. “Quite honestly, we didn’t expect to replicate these results.”

The new study, which aimed to replicate a widely shared 2011 study of 90 British university students, used pre-existing brain MRI scans from 928 individuals aged 19 to 26 whose education levels and political identities were representative of the Dutch population.

Because the Netherlands is a country with a multi-party political system, the study was also able to compare brain structures along the left-to-right continuum, unlike the British two-party system. In addition, the researchers looked at participants’ “ideology” from different angles, including their political identity and stance on socioeconomic issues, allowing them to compare brain structures along different dimensions of progressivism and conservatism.

The researchers combined the brain data with a questionnaire about the participants’ political views, which included questions about their social and economic identity (for example, how they see themselves on a sliding scale from progressive to conservative, and which political party they identify with), and questions about their social and economic ideology (for example, their stance on various social and economic issues, such as women’s and LGBQT rights, income inequality, and profit sharing).

“We view ideology as a complex, multidimensional product that includes different attitudes on social and economic issues, as well as identification with progressive or conservative ideals; it’s not just left or right,” Petropoulos says.

Consistent with the original study, the researchers found an association between conservatism and gray matter volume in the amygdala; however, this association was three times weaker compared to the original study.

“The amygdala controls the perception and understanding of threats and uncertainties related to risks. So it makes perfect sense that individuals who are more sensitive to these issues have higher security needs, which generally correspond to more conservative ideas in politics,” Petropoulos says.

The association between amygdala size and conservatism also depended on the political party with which the individual identified – for example, participants who identified with the Socialist Party, which has radically left-wing economic policies but more conservative social values, had on average more gray matter in the amygdala compared to other progressive parties.

“The Netherlands has a multi-party system, with different parties representing a spectrum of ideologies, and we find a very nice positive correlation between the political ideology of the parties and the size of that person’s amygdala,” Petropoulos says.

“This supports the idea that we’re not talking about a dichotomous representation of ideology in the brain, as between Republicans and Democrats as in the United States, but that we’re seeing a finer spectrum of how political ideology can be reflected in the anatomy of the brain.”

However, unlike the original study, the team found no association between conservatism and smaller gray matter volume in the ACC, a brain region involved in error detection, impulse control, and emotional regulation.

The researchers also extended their analysis to examine potential associations between political identity and other brain regions. This analysis revealed a positive association between gray matter volume in the right fusiform gyrus, a region of the temporal lobe critical to visual and cognitive functions, and economic and social conservatism.

“These regions are linked to facial recognition, so it makes sense that they would be involved in thinking about political issues, because political issues often remind us of the political figures who represent the ideology on those issues,” Petropoulos says. “Just remembering a politician’s face, for example, can make the fusiform gyrus light up a little bit.”

The MRI images used in this study provide information only about the anatomy of different brain regions, but the researchers say future work should incorporate information about the functional connections between the amygdala and different parts of the brain.

“I think the future of this endeavor to identify political orientations in the brain will be to look more at functional connectivity network studies and neural synchronization – how brain networks organize and synchronize across individuals, and whether there are differences in that synchronization when individuals with different political ideologies consume similar content,” Petropoulos says.