The fear of being punished makes people less likely to violate social norms, according to a study by Swiss and German researchers.
Using scanning technology, the scientists were able to show which parts of the brain react to the threat of punishment, highlighting that damage to these regions might lead to antisocial behaviour.
The study, published on Wednesday in the brain research journal Neuron, aimed to understand the effects of potential punishment on the decision-making process.
"Our societies have clear definitions of what is appropriate," said Ernst Fehr, an economist at Zurich University and one of the authors. He points to norms such as fairness, cooperation and honesty.
"Most people are willing to comply with these norms in the absence of punishment," he told swissinfo. "But a significant minority will only do so if threatened."
Fehr gives telling the truth as an example of a social norm that most people understand. That doesn't stop anyone from lying at some point though.
The researchers focused on how prepared people were to comply with the fairness norm using a money allocation game. A person had to decide how much of a certain amount of money they were prepared to share with another.
In one case, there was no punishment for an unfair division of the funds, while in the other the recipient could decide to financially punish the giver.
The activation of certain areas of the brain when punishment was an option was highlighted using so-called functional magnetic resonance imaging. This technique can show neural activity by detecting blood flow in the brain.
"People who primarily comply with a norm because of the threat of punishment probably have to suppress their egoistic impulses more strongly, which then activates this region of the frontal lobe more strongly," said Fehr.
"This result extends previous results we found showing that egoistic decisions are more likely to be made if this area of the brain is suppressed in its activity."
For the researchers, the implications of their study go beyond highlighting that some people only respond to threats. In many young people, the regions of the brain involved are not fully developed, perhaps explaining why potential punishment does not prevent anti-social behaviour.
"Our findings suggest that courts should be more careful in determining the penal responsibility of teenagers and young adults," added Fehr.
In most European countries – including Switzerland – this responsibility is set at age 18, or even 20. In the United States, it is often much lower.
The authors suggest that their findings could help understand psychopathic behaviour. They say this is because people with damage to their social compliance circuitry are incapable of behaving in appropriate ways even though they understand social norms.
But Fehr warns that using scans to determine whether someone is a danger to society is not enough.
"I think that if the brain is permanently damaged, a criminal should not be released," he told swissinfo. "But you do not lock someone up for life based on a scan; it's just one possible element that can intervene in a judgement."
He added that society plays a vital role in how norms are respected. "Our biology allows us to comply with social norms. But these norms are conditioned by society," he said.
swissinfo, Scott Capper
Functional magnetic resonance imaging (fMRI) is used to visualise brain function, by visualizing changes in chemical composition of brain areas or changes in the flow of fluids that occur over periods stretching from seconds to minutes.
In the brain, blood flow is presumed to be related to neural activity, so fMRI, like other imaging techniques, can be used to find out what the brain is doing when subjects perform specific tasks or are exposed to specific stimuli.
Procedure: a series of baseline images are taken of the brain region of interest when the subject is at rest; the subject performs a task and a second series is taken; then the first set of images is subtracted from the second, and the areas that are most visible in the resulting image are presumed to have been activated by the task.