When brain lesions occur within the brain network responsible for morality and value- based decision making, they can predispose a person toward criminal behaviour, scientists say.

Researchers examined MRI and CT scans of individuals known to have carried out crime. One group of 17 cases had a definitive correlation between criminal behaviour and a brain lesion.

A second group of 23 had an implied correlation when researchers were unsure whether the brain lesion occurred before or a er the criminal behaviour. In both groups, the lesions were in different areas of the brain.

The study, published in Proceedings of the National Academy of Sciences, is the first systemic mapping of brain lesions associated with criminal behaviour, a medical phenomenon referred to as acquired sociopathy.

It was led by Ryan Darby of Vanderbilt University Medical Center (VUMC). Researchers used neuro-images compiled from healthy volunteers organised into a “connectome” – a brain activity map.

While the lesions were in different brain areas, they were all connected to the same brain network.

“We looked at networks involved in morality as well as different psychological processes that researchers have thought might be involved; empathy, cognitive control and other processes that are important for decision making,” Darby said.

“We saw that it was really morality and value-based decision making, reward and punishment decision making that the lesions were strongly connected to,” Darby added.

“This is a relatively new approach that we have developed.”

Darby has been involved in a series of recent studies with senior author Michael Fox, assistant professor of Neurology at Harvard Medical School.

“We have previously used it to understand other disorders where it wasn’t really clear why brain lesions in different locations caused hallucinations or delusions. In those diseases, it was also found that it was a common brain network connected to the same areas. We were the first to apply this to looking at criminal behaviour.”

The study cautioned against over-interpretation of its findings, with the authors noting that violence or crime occurs in approximately nine per cent of patients with traumatic brain injury and 14 per cent of patients with a frontal lobe injury.

Older research from the UK suggests the proportion of the prison population with a brain injury may be much higher than this; with some studies citing that up to 40 per cent of prisoners have been brain injured in the past.