This is your brain on injustice: Punishing perpetrator preferred to supporting victim

By Liz Meszaros, MDLinx
Published April 12, 2018

Key Takeaways

Punishing injustice may be more rewarding to the brain than supporting the victim of that injustice, researchers suggest. Further, they found that meting out punishment for an injustice may be more acceptable when one is the recipient of wrongdoing, rather than an observer. They recently published their results in the Journal of Neuroscience.

“The perception of injustice is a fundamental precursor to many disagreements, from small struggles at the dinner table to wasteful conflict between cultures and countries. Despite its clear importance, relatively little is known about how the brain processes these violations,” wrote the authors, led by Mirre Stallen, PhD, assistant professor, Leiden University, Leiden, The Netherlands.

Dr. Stallen and fellow researchers sought to elucidate the neurobiologic mechanisms of our perceptions of injustice, as well as the ensuing punishment and compensations for injustice.

For this randomized, double-blind, placebo-controlled, between-subject study, Dr. Stallen and colleagues combined functional magnetic resonance imaging with the administration of oxytocin to develop a new decision-making task called the “Justice Game.” They included 53 males (mean age: 21.2 years), of whom 27 were given oxytocin, which has been shown to affect behavior, including promoting prosocial behavior.

The original Justice Game involved two players, one of whom is the Taker (first-party) and the other, the Partner (second-party). At the beginning of the game, both players were given 200 chips. The Taker than had the opportunity to take a maximum of 100 chips from the Partner or to not take them. The Partner had the option of punishing the Taker by spending a maximum of 100 chips of his own. For each chip spent by the Partner, the Taker’s income was reduced by 3 chips.

A variation of the game included the Observer (third-party), who could punish the Taker for his actions toward the Partner or compensate the Partner for actions against him.

All players participated in 48 trials as each participant—Taker, Partner, or Observer—for a total of 144 trials.

Before and after each task, subjects completed a questionnaire designed to determine their perceptions of fairness.

Unlike previous studies that focused on the willingness to reject unfair offers, “...the Justice Game examined how people perceive and respond to a situation in which a third-party deliberately (and unjustly) takes resources from either oneself or someone else,” noted the authors.

They found that subjects were willing to incur costs to both punish and compensate unfairness, were more likely to punish than compensate. Subjects were also more willing to spend more chips in the second-party punishment role when they themselves were the victim (Partner), than when they were the Observer and someone else was the victim.

Researchers also found that the administration of oxytocin had a stronger effect on punishment as the injustice increased. Subjects who received oxytocin expected fair treatment more often than those who did not. After oxytocin administration, 12 of 27 subjects expected other players to take no chips at all, reflecting a change in their expectations. Only 3 of 27 subjects in the placebo group changed their initial expectations.

Across all game types, the more that was taken from the Partner, the more chips were spent to either punish or compensate.

Greater activity for fairness vs unfairness was seen in the ventral medial prefrontal cortex, posterior insula, posterior cingulate, and superior temporal sulcus. Brain regions correlating with the degree of unfairness included the anterior insula (AIns), anterior cingulate cortex (ACC), dorsolateral prefrontal cortex, precuneus, and ventrolateral prefrontal cortex. Activation in these areas correlated positively with decision-making, and the higher the activation, the more punishment and compensation were meted out.

These results reflect findings from previous neuroimaging studies of fairness and unfairness.

For punishment, higher activity was seen in the ventral striatum, and for decisions to refrain from punishment for unfairness, in the temporal parietal junction (TPJ).

Willingness to punish was significantly higher in second-party games (Partner) in subjects receiving oxytocin compared with placebo. Oxytocin had no effect in third-party games (Observer). These results suggest that oxytocin may affect only the decision to punish when one is directly hurt. Researchers also observed that when frequent punishments were doled out, severe punishments were less likely.

Second-party games were more likely to increase the value of harsher punishments. Oxytocin was more likely to affect severity of punishment in both second- and third-party games.

Overall, Dr. Stallen and colleagues found that punishment was preferred over compensation, perhaps because it was more rewarding. Decisions favoring punishment over compensation increased activity in the ventral striatum, while enhanced activity in the TPJ was associated with a decision to refrain from punishment.

They also found that decisions to punish were related to the AIns, and were stronger when subjects themselves experienced the injustice, compared with observing injustice. Oxytocin did not affect decisions to compensate victims but did enhance the frequency of smaller punishments with a reduction in the willingness to punish harshly. Oxytocin may serve to shift the focus from self-interest to group interests.

“Results show that the neural mechanisms underlying punishment differ depending on whether one is directly affected by the injustice, or whether one is a third-party observer of a violation occurring to another. Specifically, the anterior insula was involved in decisions to punish following harm, whereas, in third-party scenarios, we found amygdala activity associated with punishment severity,” concluded Dr. Stallen and colleagues.

This work was supported by a grant from the European Research Council and support from the Erasmus Research Institute of Management (ERIM).

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