A new study has found a connection between injuries in certain areas of the brain and criminal behaviour.
High profile cases involving personality changes and criminality following brain injuries have highlighted this area of research in recent years.
However, there is still plenty of speculation around the role brain injuries play in instigating criminal behaviour.
The scientists used a new technique to establish links between brain injuries – known as lesions – and a “wiring diagram of the human brain”.
They applied this technique to a selection of cases in which people had undertaken criminal behaviour following brain injury.
Though the injuries had occurred in diverse brain regions, they all belonged to the same network within the brain.
"We found that this network was involved in moral decision-making in normal people, perhaps giving a reason for why brain lesions in these locations would make patients more likely to behave criminally," said Dr Richard Darby, a neurologist at Vanderbilt University who led the study.
The study, published in the journal Proceedings of the National Academy of Sciences, was based on searching the scientific literature for cases in which brain injuries were associated with crime.
In total, the scientists found 17 cases of patients who exhibited criminal behaviour after their injuries occurred, but had never exhibited such behaviour before.
They also supported their findings with a further 23 cases in which the brain injury may have preceded criminal behaviour, but not definitely.
“These provocative findings provide further support for the view that criminal behaviour can emerge from disruption to specific brain networks,” said Professor Masud Husain, a neurologist at the University of Oxford who was not involved with the study.
“Of course, there can be many other reasons why people might turn to criminality but most neurologists are familiar with patients whose decision-making, value judgments and ‘moral compass’ change following the onset of a brain disease.”
Professor Huw Williams, a neuropsychologist at the University of Exeter and who was also not involved with the study, said: “This study is fascinating and important as it shows how particular types of brain lesions may have contributed to criminality in people who were not known to have a tendency to offend before they suffered the lesion.”
But Professor Williams also emphasised the limitations of a study like this.
“The key point there is ‘might contribute’ as such lesions would not likely be a direct cause and this specific study could not confirm causality,” he said.
Other researchers pointed out that the indirect methods used by Dr Darby and his collaborators mean the results can only be viewed at preliminary.
“We need to be cautious though about some aspects of the study,” said Professor Husain.
“It is retrospective and dependent on cases reported in the literature where there was evidence of changes on brain scans,” he said.
Controlled studies with a greater number of participants would be required to draw really firm conclusions about the brain injuries identified and criminality, according to the scientists.
Dr Darby said while his results could help scientists understand how brain injuries contribute to criminal behaviour, they have their limitations.
He noted genetic, environmental and social factors are crucial, and a brain injury does not destine someone to commit crimes.
The newly emerging field of “neurolaw”, which seeks to integrate findings about the brain with legal rules and standards, is concerned partly with navigating tricky questions about responsibility in light of brain injuries.
According to Dr Darby, his work doesn’t answer these questions, but does bring them to the forefront.
"The presence of a brain lesion cannot tell us whether or not we should hold someone legally responsible for their behaviour,” he said.
“This is ultimately a question society must answer."