Punishment and revenge are as old as human existence. With the advancement of neuroscience, the processes by which humans fit the punishment to the crime has become an area of interest for scientists.

In a recent brain imaging study in Nature Neuroscience, scientists examined the brain mechanisms that underlie how people believe those who have harmed others should be punished. Researchers used functional magnetic resonance imaging (fMRI) to analyze the areas of the brain used in the process of assessing and processing emotions in punishment.

"A fundamental aspect of the human experience is the desire to punish harmful acts, even when the victim is a perfect stranger," said Rene Marois, a Vanderbilt University professor who lead the research team. "Equally important, however, is our ability to put the brakes on this impulse when we realize the harm was done unintentionally. This study helps us begin to elucidate the neural circuitry that permits this type of regulation."

Participants read scenarios in which a protagonist, John, brought intentional or unintentional harm to Steve or Mary. There were four different levels of harm: death, maiming, physical assault and property damage. There were also two versions of each scenario: one that was a factual description and another with a graphic description.

Participants were then asked to list how much punishment the protagonist deserved on a scale of zero to nine.

They found that the way in which the situation was described played a huge role in the level of punishment participants deemed appropriate for the situation, and that this was only the case if the harm was considered intentional.

"What we've shown is that manipulations of gruesome language leads to harsher punishment, but only in cases where the harm was intentional," said Michael Treadway, lead author of the study. "Language had no effect when the harm was caused unintentionally."

They found that an area of the brain called the amygdala plays a key role in processing these emotions, especially in graphic conditions and when the harm was considered intentional.

The amygdala also communicated with the dorsolateral prefrontal cortex (dlPFC), an area that is known to be critical for punishment decision making.

However, when the harm was unintentional, a different network of the brain seemed to suppress amygdala response and therefore repress the dlPFC.

"This is basically a reassuring finding," Marois said. "It indicates that when the harm is not intended, we don't simply shunt aside the emotional impulse to punishment. Instead, it appears that the brain down-regulates the impulse so we don't feel it as strongly. That is preferable because the urge to punish is less likely to resurface at a future date."