Us versus them: Outgroup damage is associated with increased activity in the brain’s reward circuits

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Summary: Aggression toward members of an “outgroup” was associated with increased activity in areas of the brain associated with reward. Activity in the ventromedial prefrontal cortex affected the amount of aggression a person displayed towards an outsider.

Source: Virginia Commonwealth University

People tend to form groups that are often in conflict with rival groups. But why do people show such a ready tendency to harm people in opposing groups?

A new study led by researchers at Virginia Commonwealth University has used functional brain imaging technology to find a possible answer: it increases activity in the brain’s reward network.

“At a time of deepening political divisions and global conflict, it is critical for us to understand why people divide one another into ‘us’ and ‘them’ and then show a deep willingness to harm ‘them,'” said the corresponding author David Chester, Ph.D., Associate Professor in the Department of Psychology at the College of Humanities and Sciences.

“Our findings further this understanding by suggesting that harming outgroup members is a relatively rewarding experience.”

The researchers had 35 male college students complete a competitive, aggressive task against either a student at their university or a supposedly competing university. In reality, the participants were unknowingly playing against a computer program, and no real people were harmed.

They found that participants who were more aggressive toward outgroup members (students from a competing university) than ingroup members (students from their own university) exhibited greater activity in the core regions of the brain’s reward circuitry—the nucleus accumbens and the ventromedial prefrontal cortex – showed decidedly how to be aggressive.

Both before and after outgroup exclusion, aggression toward outgroup members was positively associated with activity in the ventral striatum in making decisions about how aggressive to be toward their outgroup opponent.

Aggression toward outgroup members was also associated with greater activity after exclusion in the rostral and dorsal medial prefrontal cortices during provocation by their outgroup opponent. These altered patterns of brain activity suggest that frontostriatal mechanisms may play an important role in motivating aggression toward outgroup members.

The results suggest that harming outgroup members is particularly rewarding and associated with experiencing positive emotions. Such psychological reinforcement mechanisms may help explain why people appear to be so vulnerable to intergroup conflict, Chester said.

“This finding helps balance the narrative about the psychological processes underlying aggression toward outgroup members, which typically emphasizes negative emotional states such as anger and fear,” Chester said.

“This study demonstrated that positive emotions can play a role in motivating intergroup aggression, suggesting many new directions for future research on the topic and informing potential interventions aimed at reducing group conflict.”

The findings raise the possibility that one day, treatments that disrupt reward for intergroup aggression could help reduce the costly and persistent human phenomenon of intergroup violence, Chester said.

Chester is director of the Social Psychology and Neuroscience Lab at VCU, which tries to understand why people try to harm each other. In the past, the lab has focused on conflict between two individuals, attempting to eliminate any element of group membership, identity, or partisanship in carefully controlled experiments.

This new study, however, is the lab’s first foray into exploring the neural correlates of between-group aggression.

“These new findings fit well with our previous research, which has repeatedly implicated the brain’s reward circuitry (i.e., the nucleus accumbens and the ventromedial prefrontal cortex) in promoting aggressive actions,” he said.

“We advanced this line of inquiry by showing that such reward activity exerts an even greater effect during aggression in an intergroup context than in a nongroup context.”

Both before and after outgroup exclusion, aggression toward outgroup members was positively associated with activity in the ventral striatum in making decisions about how aggressive to be toward their outgroup opponent. The image is in the public domain

While the researchers were not surprised by the new findings, they were surprised to find such results even when experimenting with weak group rivalry.

“Many groups have an age-old history of deep hatred for one another, and our use of rival universities hasn’t come close to capturing what many really problematic conflicts between groups around the world look like,” Chester said.

“We chose to have such a mild rivalry between the groups for a number of reasons, one important reason being that evoking deep-seated conflict between the groups could cause undue stress to our participants. But it was still surprising to see such clear results, despite our use of relatively little intergroup rivalry.

“I suspect that our observed effect would be even stronger in the context of intergroup conflict between two groups who deeply hate each other.”

The area of ​​the brain involved in the study is not only associated with reward, but is also involved in other psychological processes such as learning, motivation and identity.

While Chester said it’s possible that brain activity doesn’t reflect the subjective experience of pleasure, decades of brain research suggests that the area’s core functions are reliably linked to rewards to the point that researchers were comfortable using the draw a conclusion, said Chester.

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More research would be needed to say definitively that the reward is the “culprit underlying the conflict between the groups,” he said.

About this news from social neuroscientific research

Author: press office
Source: Virginia Commonwealth University
Contact: Press Office – Virginia Commonwealth University
Picture: The image is in the public domain

Original research: Open access.
“Neural mechanisms of intergroup exclusion and retaliatory aggression” by Emily Lasko et al. Social Neuroscience


abstract

Neural mechanisms of intergroup exclusion and retaliatory aggression

Aggression between rival groups is frequent and violent. Although the psychological and socio-ecological determinants of intergroup aggression have been studied extensively, the neuroscience of this phenomenon remains incomplete.

To examine the neural correlates of aggression against outgroup targets (compared to ingroup targets), we recruited 35 healthy young male participants who were current or former students at the same university.

While undergoing functional MRI, participants completed an aggression task against both an ingroup and an outgroup opponent, in which their opponents repeatedly provoked them at different levels and participants were then able to retaliate.

Participants were then socially locked in and then locked out by two members of the outgroup, and then performed the same aggression task against the same two opponents. Both before and after outgroup exclusion, aggression toward outgroup members was positively associated with activity in the ventral striatum in making decisions about how aggressive to be toward their outgroup opponent.

Aggression toward outgroup members was also associated with greater activity after exclusion in the rostral and dorsal medial prefrontal cortices during provocation by their outgroup opponent.

These altered patterns of brain activity suggest that frontostriatal mechanisms may play an important role in motivating aggression toward outgroup members.

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