A groundbreaking study mapping the brain activity of video gamers has shed light on how people morally justify extreme violence.

Researchers from Monash University's social neuroscience laboratory found gamers' brain activity changed depending on whether they were shooting innocent civilians or enemy soldiers.

Doctor Pascal Molenberghs led the study and said the results provided an important insight into how people were able to commit acts of violence in real life.

"In normal everyday situations people wouldn't go out and harm other people," he said.

"But in certain situations, like, for example, during war, they have often no problems with just killing other people."

Dr Molenberghs' team asked 48 participants to watch video games where they were given a first-person perspective of the gunman.

The men and women were then told to imagine themselves as they killed innocent civilians or enemy soldiers.

Functional magnetic resonance imaging was then used to map the participants' brains as they played.

Dr Molenberghs found the test subjects had greater activity in the lateral orbitofrontal cortex, a region of the brain associated with unconscious moral decision-making, when they believed the killing was justified.

"When they were shooting innocent civilians, this brain area became very active," he said.

"But whenever they were shooting the soldiers, this area was not active at all."

The researchers were surprised to discover most of the participants could easily switch between a justified reaction and an unjustified reaction.

"People can quite easily switch off this brain area which allows them to commit violence without feeling bad about it," Dr Molenberghs said.

"There's not much complex reasoning involved in the process, so it's a very implicit kind of a process that people can quite easily switch off."

Criminals' brains could be retrained in empathy

The study also gave researchers an important understanding of how some people became desensitised to violence.

"Some people seem to have problems switching back because they have learned over a very long period to switch off their emotions," Dr Molenberghs said.

"If they then return to a normal situation where they don't fear for their lives, they have problems trying to switch it on again."

Dr Molenberghs believes the findings could one day mean the brains of violent criminals and sociopaths could be retrained to make them more empathetic.

"One of the goals of this study is to train people to become more empathetic and more morally sensitive to specific types of situations," he said.

"So you can imagine that people who commit extreme violence, through therapy and through training, can become more moral over time."

The study has been published in the journal Social Cognitive and Affective Neuroscience.