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Why the Brain Follows the Rules

Clues to understanding the human social brain come from a study of punishment's role in fairness.



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People are incredibly social beings, and we rely heavily on our interactions with others to thrive, and even survive, in the world. To avoid chaos in these interactions, humans create social norms. These rules and regulations establish appropriate and acceptable ways for us to act and respond to each other. For instance, when waiting in line, we expect people also to wait their turn. As a result, we get upset when someone decides to cut in line: they violated a social norm.

But how are social norms maintained? And what makes us comply with social norms? Primarily, the answer is that, if we don’t follow the rules, we might get in trouble. Numerous studies demonstrate that, when the threat of punishment is removed, people tend to disregard social norms. The neat and orderly line disintegrates.

It remains unclear, however, how the brain processes the threat of punishment when deciding whether or not to comply with a social norm. A recent study conducted by neuroscientist Manfred Spitzer and his colleagues at the University of Ulm in Germany and the University of Zurich in Switzerland tried to shed light on this mystery. The researchers put 24 healthy male students in a functional magnetic resonance imaging (fMRI) scanner to see what parts of the brain were activated during a two-person social exchange with real monetary stakes.

In this game, a research participant (“Person A”) was given money, and had to decide how much he wanted to give to another person (“Person B”) and how much he wanted to keep. In one variation of the game—the “punishment threat condition"—Person B could punish Person A if he or she believed that Person A had divided the money unfairly, or violated the “fairness social norm.” In another situation, there was no punishment threat and Person A could act freely without worrying about the consequences. The researchers sought to find out how much more money Person A would give to Person B under the threat of punishment, and what brain circuits are associated with this change in behavior. 

Not surprisingly, the threat of punishment made people act more fairly. In the “punishment threat condition” people split the money close to equally. However, when Person B had no recourse, the people given the money acted very differently and gave away, on average, less than 10 percent of the money.

One of the interesting things about social norm compliance, however, is that there is tremendous individual variation. Some people would never cut in line or act unfairly, whereas others don’t think twice about it. Using a questionnaire, the researchers measured each participant’s “Machiavellism,” a combination of selfishness and opportunism, which is often used to describe someone’s tendency to manipulate other people for personal gain. Sure enough, the people with high Machiavellism scores gave less money away when there was no punishment threat and were best at avoiding punishment when the threat of punishment was present. Therefore, these individuals earned the most money overall.

When the researchers looked at the brain activity of people playing this simple game, they found a consistent pattern. One region in the frontal lobes, the orbitofrontal cortex, seemed to be responsible for evaluating the potential for punishment. In other words, it figured out whether or not violating the social norm would get us in trouble. A second brain region, the dorsolateral prefrontal cortex, was responsible for inhibiting the natural tendency to keep most of the money (this would be the greedy thing to do) if this action might lead to future punishment. Interestingly, these brain areas only were activated when the threat of punishment came from a real person, and not a computer that was programmed to act like a real person.

Furthermore, just as Machiavellism personality traits influenced how people behave, these traits also relate to what is happening in the brain. The orbitofrontal cortex was most activated in the more self-interested, opportunistic people. This finding makes sense because, if the orbitofrontal cortex is helping people detect and evaluate threats, then it should be most active in people who are worried about getting punished. This study can also help us understand what might be happening in the brains of people who struggle to follow social norms, which is what happens in mental illnesses such as psychopathy and antisocial personality disorder.

Of course, many different variables not studied in this experiment can also affect social norm compliance. Even a norm as seemingly straightforward as “fairness” can get pretty complicated pretty quickly. The social norm of fairness, after all, does not always mean an equal distribution of goods. Someone may deserve more based on effort, talent or simply the feeling of entitlement that comes from social status. For instance, one could argue that in the non-punishment situation, Person A was put in a position of power, because he or she was given complete control of the money. On the other hand, when Person B is given the right to punish Person A, Person B is now put in a superior position of power. And accordingly, the social norm for Person A changes: it is no longer acceptable for him to keep all the money for himself. This adjustment suggests that the brain activity evident in the Spitzer study could, in part, be related to changes in power and status between the punishment and non-punishment condition. In fact, in a recent study, we found that the dorsolateral prefrontal cortex was more activated when interacting with a person who is in superior social position.

We may have a long road ahead to understand the complexity of the brain mechanism underlying human social behavior fully, but Spitzer and his colleagues should certainly be commended for their efforts and well-designed research experiment on social norm compliance. Although questions remain and the interpretations are not completely straightforward, this study takes us one step closer to solving the puzzle of the social brain.

Mind Matters is edited by Jonah Lehrer, the science writer behind the blog The Frontal Cortex and the book Proust was a Neuroscientist.

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