Humans tend to form groups, which often find themselves 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 used functional brain imaging technology to reveal a potential answer: It increases activity in the brain’s reward network.
“At a time of deepening political divisions and global conflict, it is crucial for us to understand why people divide each other up into ‘us’ and ‘them’ and then show a profound willingness to harm ‘them,'” said corresponding author David Chester, Ph.D., an associate professor in the Department of Psychology in the College of Humanities and Sciences. “Our findings advance 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 from their university or from what they were told was a rival university. In reality, participants unknowingly played against a computer program, and no real people were harmed.
They found that participants who were more aggressive against outgroup members (students from a rival university) versus ingroup members (students from their own university) exhibited greater activity in core regions of the brain’s reward circuit — the nucleus accumbens and ventromedial prefrontal cortex — while they decided how aggressive to be.
Both before and after outgroup exclusion, aggression toward outgroup members was positively associated with activity in the ventral striatum during decisions about how aggressive to be toward their outgroup opponent. Aggression toward outgroup members was also linked to greater post-exclusion activity in the rostral and dorsal medial prefrontal cortex during provocation from their outgroup opponent. These altered patterns of brain activity suggest that frontostriatal mechanisms may play a significant role in motivating aggression toward outgroup members.
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