From where does the thirst for justice come? It seems that third-party punishment of wrongdoers is common to all human cultures. But animals, even non-human primates, don't seem to have the same desire to punish those who haven't personally wronged them but who have wronged others. Is punitive justice uniquely human? A new theory authored by scientists from Yale and Vanderbilt offers a neurobiological model for the evolution of third-party punishment in human societies.

While it is often assumed that legal decision-making is purely based on rational thinking, research suggests that much of the motivation for punishing is driven by negative emotional responses to the harm. This signal appears to be generated in the amygdala, causing people to factor in their emotional state when making decisions instead of making solely factual judgments. Next, the decision-maker must integrate his or her evaluation of the norm-violator's mental state and the amount of harm with the specific set of punishment options. The researchers propose that the medial prefrontal cortex, which is centrally located and has connections to all the other key areas, acts as a hub that brings all this information together and passes it to the dorsolateral prefrontal cortex (DLPFC), where the final decision is made with the input from another rear-brain area called the intraparietal sulcus, involved in selecting the appropriate punishment response. As such, the DLPFC may be at the apex of the neural hierarchy involved in deciding on the appropriate punishments that should be given to specific norm violations.

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