Brain lesions can make people prone to committing crimes if they occur within the network responsible for morality and value-based decision-making, a study has found.
The study, published in the journal PNAS, is the first systemic mapping of brain lesions associated with criminal behaviour - a medical phenomena referred to as acquired sociopathy.
Famous cases of acquired sociopathy include Phineas Gage, a railroad worker who in 1848 exhibited anti-social behaviour after surviving an explosive blast that sent an iron rod through his brain, and Charles Whitman, the "Texas Tower Sniper," who had a brain tumour and murdered 16 people in 1966.
Researchers at Vanderbilt University Medical Center (VUMC) in the US reviewed more recent cases of brain lesions associated with criminal behaviour, examining MRI and CT scans of those individuals.
One group of 17 cases had a definitive correlation between criminal behaviour and a brain lesion.
A second group of 23 cases had an implied correlation when researchers did not know whether the brain lesion occurred before or after the criminal behaviour.
In both groups, the lesions were at different areas of the brain.
The researchers used neuroimaging analyses - large datasets compiled from healthy volunteers organised into a connectome, similar to a map of brain activity.
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," said Ryan Darby, assistant professor at VUMC.
"We saw that it was really morality and value-based decision making - reward and punishment decision making - that the lesions were strongly connected to," said Darby, who did the research during a fellowship at Harvard Medical School in the US.
Lesions in patients with criminal behaviour were more strongly connected to this moral decision-making network than lesions in patients without criminal behaviour, suggesting that connectivity to this network was specific to criminal behaviour.
"This is a relatively new approach that we have developed," Darby said.
"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," said Darby.
"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," he said.
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