Dr. Molly Crockett, a neuroscientist and experimental psychologist at Oxford University, explains why we often punish others even if it hurts ourselves, how populist movements capitalise on our thirst for retaliation, and what responsible leaders can do to stop the cycle of retribution.

In your research, you study the neuroscience and psychology of retaliation. What have you discovered?

The biggest takeaway from this research is that social emotions like anger, envy, and spite are very powerful motives. They often outweigh economic self-interest and they tap into the brain's reward centres – the same brain areas that play a role in addiction. These emotions can fuel a behavior called 'costly punishment': where people take on a personal cost to punish another person for being unfair.

One speculation is that this destructive impulse to punish may be even stronger when people are under chronic stress, for example during an economic recession.

How did you find out about this impulse?

Costly punishment has been demonstrated in an experiment called the ultimatum game. In this game, one player (the “proposer”) is given some money and can decide how to split it with a second player (the “responder”). The responder can then accept the offer and take their share of the money, or they can reject it, in which case, the money disappears and neither player gets anything.

The research shows that most responders will reject offers they consider to be unfair (usually about less than 30% of the total pie). When this experiment was first conducted in the early 1980s, the results surprised most economists, because the results contradicted classical models of “rational self interest”. Over decades of research, this has proven to be one of the most robust findings in behavioural science: people care about far more than material self-interest. They care about fairness, they care about autonomy and identity, and they don't like being treated with disrespect. People find that destroying the wealth of a more powerful player is much more satisfying than taking a small offer they see as insulting.

You've studied the neuroscience behind this. How does our brain make the decision to inflict costly punishment?

When people reject unfair offers, a brain area called the dorsal stratum is activated. The dorsal stratum is at the core of the reward system of the brain. It's activated when we receive all kinds of rewards, for example money, food, or seeing nice pictures. It's also very strongly implicated in addiction. An initial hit of cocaine, for example, causes a response in the striatum. As people become addicted, any cue associated with taking cocaine also activates the striatum. The fact that this same brain area is activated during costly punishment suggests there could be an addictive quality to punishment and retribution.

According to our experiments, people are also more likely to reject unfair offers if their brain has been depleted of serotonin, a neurotransmitter involved in self-regulation. When serotonin levels are low, people become more focused on immediate rewards, and they become more impulsive and aggressive.

What can we do to control this destructive behaviour?

First of all, because the brain circuitry involved in punishment has also been implicated in addiction, it's very important not to indulge the impulse for revenge. Retaliation can breed more retaliation. When two groups are in conflict, and one side retaliates, the other side becomes more likely to retaliate. As this behavior escalates it could take on an addictive quality. Each time you indulge the impulse makes it more likely you'll do it again the next time.

Also - and this is more speculative - animal studies have shown that serotonin levels can be depleted by long-term stress. So the hypothesis is that chronic stress, which might be one consequence of an economic recession, could prime people to be in a state where they are more likely to engage in these retributive behaviours.

What if people feel they are acting out of a sense of justice rather than revenge?

Punishment is often described in moralistic, high-minded terms: punish unfairness, stand up to economic injustice. But in our research, people punished even when the experiment had been set up so that the punishment was hidden - the perpetrator never found out they had been punished. There was no social message in the punishment, no lesson for the perpetrator. People just wanted to hurt the person who had hurt them, and that's an anti-social motive.

We also find that people seem to be largely unaware of their own motives for punishment. When asked about why they punish, they are more likely to cite moralistic reasons like enforcing fairness norms, than antisocial motives like a desire for revenge. And self-reported desire for revenge is totally uncorrelated with vengeful behavior. This suggests people might be punishing for antisocial reasons, but telling themselves and others they are punishing for moralistic reasons.

Is there a link between the individual impulse to punish, and the global rise in populist movements?

Populist messaging has been very effective in channelling retributive impulses into votes. Around the world populist movements are wreaking economic destruction and social turmoil in the name of moral principles. That may be the story people are telling themselves and others, but it's likely not the only motive. One responsibility of leaders is to be careful not to let harmful, destructive behaviour be justified on moral grounds.

What else can responsible leaders do to stop the cycle of retribution?

Ultimatum game experiments have shown that if responders are given an alternative channel for expressing their dissatisfaction with unfair offers, for example by sending a written message to the proposer, then they will send that message and accept the offer. They sent angry messages like “Thanks for nothing”, “Why do you have to be greedy?” - but they accepted the offer.

When people feel that destructive behavior is the only option they have to make their voices heard, they are going to take that option, even if it hurts them financially. But if they have alternative channels to express their displeasure, they may be able to act in a way that's consistent with their long-term economic interest and still feel satisfied.

That's fascinating. But don't we have more channels than ever before to express our dissatisfaction in public?

This is a puzzle that we have not yet solved. On the one hand, research has shown that giving people alternative channels to express their displeasure makes them less likely to punish. But on the other hand, research on aggression shows that “venting” makes people more likely to be aggressive in the future. If expressing outrage is rewarding, small acts of self-expression, for instance on Facebook or Twitter, might increase the likelihood of future expressions of outrage – perhaps via one’s vote.

What's next for your research?

I would like to test the hypothesis that punishment has an addictive quality. If it does, then perhaps we can learn from addiction research how to counter the punitive impulse.