The punishment should fit the crime. This universal concept underlies any reasonable justice system.
But the foundations of our sense of justice might be more precarious than we might imagine, given that scientists have figured out how to tinker with the part of the brain that deals with punishment.
According to a study published in the journal Neuron, two different regions of the brain separately deal with judgement of guilt or innocence and assessment of punishment. By stimulating the latter, researchers at Vanderbilt University and Harvard University figured out a way to influence penalty decisions.
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In experiments involving 66 male and female volunteers, researchers asked study participants to assess a series of scenarios in which a suspect committed a crime, the resulting damage of which ranged from property loss to severe injury and even death.
The part of the brain that deals with punishment decisions is the dorsolateral prefrontal cortex. In half of the study participants, the scientists used repetitive transcranial magnetic stimulation (rTMS), a painless process involving an electromagnet placed on the scalp to temporarily affect cognitive activity, on that region of the brain. The other half of the study participants received a placebo.
What researchers found is that rTMS manipulation changed the way participants assessed penalties for various crimes. While the study's volunteers universally factored in guilt and the level of harm in a crime in their punishment assessments, those who received rTMS opted for significantly lower punishments for guilty criminals than participants who received the placebo.
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"This research gives us deeper insights into how people make decisions relevant to law, and particularly how different parts of the brain contribute to decisions about crime and punishment," co-author Owen Jones, professor at Vanderbilt and director of the MacArthur Foundation Research Network on Law and Neuroscience, said in a statement.
This study builds on previous work identifying the pathways and cognitive processes of judgement and justice in the brain. Humans are undoubtedly a cooperative species, but our ability to assess guilt and hand out justice to those who don't go along with social norms is also important to our success as in forming large-scale societies.
A study published in 2011 in the journal PLoS Biology looked at neurological activity during a game involving economic decision-making. One player is asked how to share a fixed sum of money with another player. The second player can either accept the proposal and split the money accordingly, or reject it, and both of the players take home nothing.
If the offer is to share the money equally, the second player always accepts. Any time one player offers an unfair suggestion to his or her counterpart, however, with the split favoring the first player, the second player rejects the offer half of the time, even though that means the second player lost money, too. This inequitable offer triggers an automatic response in the amygdala of the brain, which deals with fear and anger and helps to explain the reaction of the second player to a sense of unfairness.
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The PLoS Biology study is an example of second-party punishment, in which the victim directly punishes the accuser. The results suggest that emotion plays a role when the party directly experiences the outcome. But third-party punishment, a uniquely human trait, is largely guided by reason, found a study published last year in the Journal of Neuroscience.
In an exercise where study participants were subjected to functional magnetic resonance imaging (fMRI) brain-scanning while evaluating situations meant to invoke a sense of justice, researchers found that people with high "justice sensitivity," a measure determined by responses to a questionnaire, showed higher-than-average activity in parts of the brain linked higher-order cognition. Areas of the brain tied to emotion, on the other hand, were unaffected.
Taken together, these studies show that justice is hard-wired into our brains, and with the latest research, scientists may have found a way to short circuit it.