As a kid you probably found some decisions by your parents utterly unjust. Perhaps you proclaimed, “That’s not fair!” when you were forced to eat spinach, or if your sibling got something you didn’t. As adults, we still experience intense sensations of injustice, sometimes in response to more serious issues such as human rights, health care access and gun control. Perceived injustice often leads to disagreements ranging from family spats to conflicts within and between nations, but little is known about the biology of how the brain responds to feelings of injustice. A recent collaborative study1 from several institutions in the Netherlands and researchers at the University of California San Diego sought to better understand how humans perceive and respond to injustice.

The Justice Game

First, the 54 participants were exposed to “fair” and “unfair” situations in a computer simulation called The Justice Game. The game includes two players: the Taker and the Partner, with the study participants assigned the role of Partner. To start, the Taker and Partner are each given an equal number of chips. The Taker can decide to take anywhere from zero to 100 chips from the Partner. Then the Partner can “punish” the Taker by spending the Taker’s chips. While the game is being played, active brain regions are monitored and recorded via fMRI, a technique that measures brain activity by detecting biochemical changes related to blood flow.

Punishment as Reward

When no chips were taken from the Partner (the “fair” condition), brain regions associated with self-control and social perception were active in most participants. When the Taker did take chips from the Partner (“unfair” condition), emotion- and reward anticipation-related regions were active. Further, when the Partner decided to punish the Taker, this resulted in strong activation of the ventral striatum, a region associated with reward and addiction.2  Overall, these results suggest that we respond very emotionally to perceived injustice (no surprise there) and that our brains interpret punishment as a reward for those who are inflicting it.

Victim or Observer

The investigators also wanted to know how these responses differ when the study participant is a third party observer, rather than a direct participant in the game. They modified the Justice Game so that the participants were set up to watch the fair or unfair decisions made by the Taker and had the option to punish him or her just as the Partner could. In this scenario both the Taker and the Partner are nonparticipants. The study found that the participants were more likely to punish as a victim than as a third party observer. This finding might suggest that acts of injustice committed against oneself are perceived as more severe than those committed against others.

Punishment or Compensation

In a third version of the game, the observer had the option to punish the Taker or help the Partner by giving the Partner chips. When given the choice, the participants were more likely to punish the transgressor than compensate the victim. Since punishment activates the reward-related regions in our brain, it may be experienced as more rewarding than compensating the victim.

The Influence of Oxytocin

Lastly, the authors explored the influences of oxytocin, a hormone known to promote bonding and trust.3 Oxytocin is often released when people bond physically, such as loved ones cuddling or a mother nursing her baby. Participants were given oxytocin or a placebo via nasal spray before the Justice Game. Oxytocin increased the administration of low-level punishments from both victims and third party observers. This suggests that the hormone decreased the willingness of the participants to punish harshly.  Considering this, it’s possible that more physical social interaction could help decrease the administration of a harsh punishment by parents, teachers or even world leaders.

The results from this innovative, collaborative study could be viewed as bleak or as hopeful. What does it say about human nature that we perceive punishing other people as a reward and that we prefer to punish wrongdoers than help victims? Alternatively, these results could be interpreted as suggesting that humans have a very strong emotional response to injustice and an ardent drive to right wrongs. The oxytocin data suggest that physical social interaction may influence our reactions to injustice, diminishing our inclinations to punish harshly. Overall, these experiments provide insights into neurological mechanisms that govern injustice and demonstrate a technique to continue studying this area in the future.

References

  1. Stallen, M., Rossi, F., Heijne, A., Smidts, A., De Dreu, C. K., & Sanfey, A. G. (2018). Neurobiological mechanisms of responding to injustice. Journal of Neuroscience, 1242-17.
  2. Knutson, B., & Cooper, J. C. (2005). Functional magnetic resonance imaging of reward prediction. Current Opinion in Neurology, 18(4), 411-417.
  3. Graustella, A. J., & MacLeod, C. (2012). A critical review of the influence of oxytocin nasal spray on social cognition in humans: evidence and future directions. Hormones and Behavior, 61(3), 410-418.

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