Researchers at the American College of Greece and the University of Amsterdam have found that subtleties in political ideology might be linked to brain structure.
Specifically, the findings reveal that conservative voters tend to have slightly larger amygdalas—around the size of a sesame seed—than their progressive counterparts.
Published on September 19th in the journal iScience, the new research revisits a decade-old theory with a much larger and more diverse sample size. While confirming the link between conservatism and amygdala size, the study validates previous findings but uncovers new complexities in the relationship between brain anatomy and political beliefs.
“It was really a surprise that we replicated the amygdala finding,” said Diamantis Petropoulos Petalas, a American College of Greece professor and the study’s lead author. “Quite honestly, we did not expect to replicate any of these findings.”
The amygdala is a small, almond-shaped cluster of neurons located deep within the brain’s temporal lobe. It plays a crucial role in processing emotions, particularly those related to fear, threat detection, and emotional responses. The amygdala helps individuals perceive and respond to potential environmental dangers, influencing decision-making under uncertainty and regulating reactions to stress.
Because it is involved in processing fear and risk, the amygdala is often associated with behaviors linked to security and caution, which may explain its connection to political conservatism, as observed in the recent study.
Previous Ideas about Political Ideologies and Brain Size
For the past decade, scientists have been trying to find any connections between political stances and brain size. In a 2010 study by the University of College London, researchers asked participants to label their political leanings from extreme conservative to extreme liberal before receiving an MRI scan. Their analysis showed a loose correlation between the two variables at that time.
“People with liberal views tended to have increased grey matter in the anterior cingulated cortex, a region of the brain linked to decision-making, in particular when conflicting information is being presented,” the study reported. “Previous research showed that electrical potentials recorded from this region during a task that involves responding to conflicting information were bigger in people who were more liberal or left-wing than people who were more conservative.”
Updated Findings
The new study aimed to build on the UCL 2011 study, which had a relatively small sample size of 90 UK university students. In contrast, this new project analyzed pre-existing MRI brain scans from 928 individuals aged 19-26, representing a much broader cross-section of the Dutch population. This larger sample allowed for more nuanced comparisons across the political spectrum, mainly since the Netherlands’ multi-party system offers a broader range of political affiliations than the two-party system in the UK or US.
The study paired MRI data with questionnaires exploring participants’ social and economic ideologies. This approach allowed researchers to investigate political identity from various angles, including how participants aligned themselves on progressive versus conservative ideals and where they stood on key socioeconomic issues like LGBTQ rights and income inequality.
The study reaffirmed the link between conservatism and the volume of gray matter in the amygdala, a brain region involved in processing threats and uncertainties. However, the association was notably weaker than in the original study.
“The amygdala controls for the perception and the understanding of threats and risk uncertainty, so it makes a lot of sense that individuals who are more sensitive towards these issues have higher needs for security, which is something that typically aligns with more conservative ideas in politics,” explained Petropoulos Petalas.
Political ideologies A More Nuanced Relationship
Interestingly, the association between amygdala size and conservatism varied depending on the political party the individual identified with. For instance, participants who identified with the Dutch Socialist Party, which has left-wing economic policies but conservative social values, had larger amygdalas than those affiliated with other progressive parties. This variability suggests that political ideology cannot be reduced to a simple left-right dichotomy but has a more nuanced relationship.
“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 parties’ political ideology and the amygdala size of that person,” said Petropoulos Petalas. “That speaks to the idea that we’re not talking about a dichotomous representation of ideology in the brain, such as Republicans versus Democrats as in the US, but we see a more fine-grained spectrum of how political ideology can be reflected in the brain’s anatomy.”
Despite confirming the amygdala connection, the study did not replicate the original finding that linked political ideologies of conservatism with a smaller volume of gray matter in the anterior cingulate cortex (ACC), a region involved in impulse control and emotional regulation. This discrepancy may point to the complexity of the relationship between brain anatomy and political ideology, suggesting that earlier findings might not generalize across populations and instead occur on a case-by-case basis.
Kenna Hughes-Castleberry is the Science Communicator at JILA (a world-leading physics research institute) and a science writer at The Debrief. Follow and connect with her on X or contact her via email at kenna@thedebrief.org