Lefty or righty? A new study links a larger anterior cingulate cortex (left) to politically liberal views and a larger right amygdala to conservatism.

R. Kanai et al., Current Biology, 21 (26 April 2011)

Does Your Brain Bleed Red, White, and Blue?

Politics can be a touchy topic, especially when it comes to neuroscience. Researchers who've dared to tackle questions about how people's political leanings might be reflected in the brain have often earned scoffs and scoldings from their colleagues. A provocative new study is likely to be no exception. It claims to find features of brain anatomy that differ between people who identify themselves as politically conservative or politically liberal.

Cognitive neuroscientist Ryota Kanai and colleagues at University College London recruited 90 student volunteers and had them rate their political philosophy on a five-point scale ranging from very liberal to very conservative. Then the researchers used magnetic resonance imaging to get a look inside their brains. In a paper published online today in Current Biology, the team reports two main findings: political conservatives tend to have a larger right amygdala, a region involved in detecting threats and responding to fearful stimuli, whereas liberals tend to have a larger anterior cingulate cortex, an area that becomes active in situations involving conflict or uncertainty.

There was considerable overlap though. When the researchers looked only at the brain scans, Kanai says they could predict who was liberal and who was conservative with about 75% accuracy—much better than a coin toss but probably not good enough for any high-tech campaign tactics.

Kanai is at pains to make clear that the findings don't mean political views are "hard-wired" into the brain. He acknowledges that the data don't prove that these neuroanatomical differences actually cause political differences, but he suspects that they might play a role. He says psychological studies suggest that conservatives are more sensitive to negative emotions like fear and disgust, whereas liberals are more tolerant of situations involving conflict and uncertainty. (To armchair psychologists, this might explain some stereotypical behavior, such as the spike in blood pressure a hard-core conservative might experience when Fox News plays a new recording from Osama bin Laden, or the half-hour it might take an Earth-loving liberal to decide whether to buy the organic apple flown in from Chile or the local apple treated with pesticides.) Kanai speculates that subtle size differences in the amygdala and anterior cingulate might predispose people to particular "cognitive styles or personality traits" that in turn make them gravitate toward a particular worldview.

"It's provocative," says social cognitive neuroscientist David Amodio of New York University. Amodio is no stranger to political neurocontroversy. A paper he published in Nature Neuroscience in 2007 resulted in some hyperbolic headlines and punditry in the mainstream media and a critical backlash from skeptical neuroscience bloggers. In that study, when Amodio and colleagues used electroencephalography to investigate brain activity, they found a correlation between greater activity in the anterior cingulate and political liberalism. The picture that emerges from that work, Kanai's study, and other research is that "even complex political views are probably rooted in more basic psychological and brain processes," Amodio says.

It's an appealing story and a topic worth investigating, says cognitive neuroscientist Martha Farah of the University of Pennsylvania. But there's plenty of reason to be cautious, she says. For one, it's not clear what a bigger amygdala—or a bigger anything in the brain—actually means in terms of brain function and behavior. The research, she says, is unclear and often contradictory on this point.

Another problem is that most brain regions have multiple functions, Farah says: "Who says fear is the only function of the amygdala?" She notes that this brain region also responds to sexually arousing images and pictures of happy faces, and one recent study found a correlation between amygdala volume and the size of people's social networks. Likewise, the anterior cingulate cortex has been implicated in a long list of cognitive functions. By picking and choosing from the previous studies, "they're indulging in a bit of just-so storytelling," Farah says.