In 1968 a debate was held between conservative thinker William F. Buckley, Jr., and liberal writer Gore Vidal. It was hoped that these two members of opposing intellectual elites would show Americans living through tumultuous times that political disagreements could be civilized. That idea did not last for long. Instead Buckley and Vidal descended rapidly into name-calling. Afterward, they sued each other for defamation.

The story of the 1968 debate opens a well-regarded 2013 book called Predisposed, which introduced the general public to the field of political neuroscience. The authors, a trio of political scientists at the University of Nebraska-Lincoln and Rice University, argued that if the differences between liberals and conservatives seem profound and even unbridgeable, it is because they are rooted in personality characteristics and biological predispositions.

On the whole, the research shows, conservatives desire security, predictability and authority more than liberals do, and liberals are more comfortable with novelty, nuance and complexity. If you had put Buckley and Vidal in a magnetic resonance imaging machine and presented them with identical images, you would likely have seen differences in their brain, especially in the areas that process social and emotional information. The volume of gray matter, or neural cell bodies, making up the anterior cingulate cortex, an area that helps detect errors and resolve conflicts, tends to be larger in liberals. And the amygdala, which is important for regulating emotions and evaluating threats, is larger in conservatives.

While these findings are remarkably consistent, they are probabilities, not certainties—meaning there is plenty of individual variability. The political landscape includes lefties who own guns, right-wingers who drive Priuses and everything in between. There is also an unresolved chicken-and-egg problem: Do brains start out processing the world differently or do they become increasingly different as our politics evolve? Furthermore, it is still not entirely clear how useful it is to know that a Republican’s brain lights up over X while a Democrat’s responds to Y.

So what can the study of neural activity suggest about political behavior? The still emerging field of political neuroscience has begun to move beyond describing basic structural and functional brain differences between people of different ideological persuasions—gauging who has the biggest amygdala—to more nuanced investigations of how certain cognitive processes underlie our political thinking and decision-making. Partisanship does not just affect our vote; it influences our memory, reasoning and even our perception of truth. Knowing this will not magically bring us all together, but researchers hope that continuing to understand the way partisanship influences our brain might at least allow us to counter its worst effects: the divisiveness that can tear apart the shared values required to retain a sense of national unity.

Social scientists who observe behaviors in the political sphere can gain substantial insight into the hazards of errant partisanship. Political neuroscience, however, attempts to deepen these observations by supplying evidence that a belief or bias manifests as a measure of brain volume or activity—demonstrating that an attitude, conviction or misconception is, in fact, genuine. “Brain structure and function provide more objective measures than many types of survey responses,” says political neuroscientist Hannah Nam of Stony Brook University. “Participants may be induced to be more honest when they think that scientists have a ‘window’ into their brains.” That is not to say that political neuroscience can be used as a tool to “read minds,” but it can pick up discrepancies between stated positions and underlying cognitive processes.

Brain scans are also unlikely to be used as a biomarker for specific political results because the relationships between the brain and politics is not one-to-one. Yet “neurobiological features could be used as a predictor of political outcomes—just not in a deterministic way,” Nam says.

To study how we process political information in a 2017 paper, political psychologist Ingrid Haas of the University of Nebraska-Lincoln and her colleagues created hypothetical candidates from both major parties and assigned each candidate a set of policy statements on issues such as school prayer, Medicare and defense spending. Most statements were what you would expect: Republicans, for instance, usually favor increasing defense spending, and Democrats generally support expanding Medicare. But some statements were surprising, such as a conservative expressing a pro-choice position or a liberal arguing for invading Iran.

Haas put 58 people with diverse political views in a brain scanner. On each trial, participants were asked whether it was good or bad that a candidate held a position on a particular issue and not whether they personally agreed or disagreed with it. Framing the task that way allowed the researchers to look at neural processing as a function of whether the information was expected or unexpected—what they termed congruent or incongruent. They also considered participants’ own party identification and whether there was a relationship between ideological differences and how the subjects did the task.

Liberals proved more attentive to incongruent information, especially for Democratic candidates. When they encountered such a position, it took them longer to make a decision about whether it was good or bad. They were likely to show activation for incongruent information in two brain regions: the insula and anterior cingulate cortex, which “are involved in helping people form and think about their attitudes,” Haas says. How do out-of-the-ordinary positions affect later voting? Haas suspects that engaging more with such information might make voters more likely to punish candidates for it later. But she acknowledges that they may instead exercise a particular form of bias called “motivated reasoning” to downplay the incongruity.

Motivated reasoning, in which people work hard to justify their opinions or decisions, even in the face of conflicting evidence, has been a popular topic in political neuroscience because there is a lot of it going around. While partisanship plays a role, motivated reasoning goes deeper than that. Just as most of us like to think we are good-hearted human beings, people generally prefer to believe that the society they live in is desirable, fair and legitimate. “Even if society isn’t perfect, and there are things to be criticized about it, there is a preference to think that you live in a good society,” Nam says. When that preference is particularly strong, she adds, “that can lead to things like simply rationalizing or accepting long-standing inequalities or injustices.” Psychologists call the cognitive process that lets us do so “system justification.”

Nam and her colleagues set out to understand which brain areas govern the affective processes that underlie system justification. They found that the volume of gray matter in the amygdala is linked to the tendency to perceive the social system as legitimate and desirable. Their interpretation is that “this preference to system justify is related to these basic neurobiological predispositions to be alert to potential threats in your environment,” Nam says.

After the original study, Nam’s team followed a subset of the participants for three years and found that their brain structure predicted the likelihood of whether they participated in political protests during that time. “Larger amygdala volume is associated with a lower likelihood of participating in political protests,” Nam says.  “That makes sense in so far as political protest is a behavior that says, ‘We’ve got to change the system.’”

Understanding the influence of partisanship on identity, even down to the level of neurons, “helps to explain why people place party loyalty over policy, and even over truth,” argued psychologists Jay Van Bavel and Andrea Pereira, both then at New York University, in Trends in Cognitive Sciences in 2018. In short, we derive our identities from both our individual characteristics, such as being a parent, and our group memberships, such as being a New Yorker or an American. These affiliations serve multiple social goals: they feed our need to belong and desire for closure and predictability, and they endorse our moral values. And our brain represents them much as it does other forms of social identity.

Among other things, partisan identity clouds memory. In a 2013 study, liberals were more likely to misremember George W. Bush remaining on vacation in the aftermath of Hurricane Katrina, and conservatives were more likely to falsely recall seeing Barack Obama shaking hands with the president of Iran. Partisan identity also shapes our perceptions. When they were shown a video of a political protest in a 2012 study, liberals and conservatives were more or less likely to favor calling police depending on their interpretation of the protest’s goal. If the objective was liberal (opposing the military barring openly gay people from service), the conservatives were more likely to want the cops. The opposite was true when participants thought it was a conservative protest (opposing an abortion clinic). The more strongly we identify with a party, the more likely we are to double down on our support for it. That tendency is exacerbated by rampant political misinformation and, too often, identity wins out over accuracy.

If we understand what is at work cognitively, we might be able to intervene and try to ease some of the negative effects of partisanship. The tension between accuracy and identity probably involves a brain region called the orbitofrontal cortex, which computes the value of goals and beliefs and is strongly connected to memory, executive function and attention. If identity helps determine the value of different beliefs, it can also distort them, Van Bavel says. Appreciating that political affiliation fulfills an evolutionary need to belong suggests we should create alternative means of belonging—depoliticizing the novel coronavirus by calling on us to come together as Americans, for instance. And incentivizing the need to be accurate could increase the importance accorded that goal: paying money for accurate responses or holding people accountable for incorrect ones have been shown to be effective.

It will be nearly impossible to lessen the partisan influences before the November 3 election because the volume of political information will only increase, reminding us of our political identities daily. But here is some good news: a large 2020 study at Harvard University found that participants consistently overestimated the level of out-group negativity toward their in-group. In other words, the other side may not dislike us quite so much as we think. Inaccurate information heightened the negative bias, and (more good news) correcting inaccurate information significantly reduced it.

“The biology and neuroscience of politics might be useful in terms of what is effective at getting through to people,” Van Bavel says. “Maybe the way to interact with someone who disagrees with me politically is not to try to persuade them on the deep issue, because I might never get there. It’s more to try to understand where they’re coming from and shatter their stereotypes.”