Brain lesions contribute to criminal behaviour

Ed Gein was repeatedly beaten around the head by his alcoholic father. Gary Heidnik fell from a tree at age six and hit his head hard enough to deform his skull. Jerry Brudos, electrocuted as a 21-year-old, complained of recurring migraine headaches and blackouts. Edmund Kemper suffered a head injury after crashing his motorcycle.

These four individuals, among the half-dozen infamous serial killers whose crimes inspired the fictional character Buffalo Bill in the movie The Silence of the Lambs, demonstrate the frequency of suspected brain injuries as potential contributing to the making of the very worst criminals. 

Now research led by neurologist Ryan Darby, of Vanderbilt University Medical Centre in Nashville, Tennessee, US, has shed light on how brain ‘lesions’ – identifiable injuries caused by trauma, stroke or tumours – contribute to criminal behaviour, through damaging not just one specific area but any number of regions involved in the complex networked neurological processes of higher human brain function.  

Based on mapping the brains of 17 individuals convicted of crimes ranging from fraud and theft to assault, rape and murder – the research, published in Proceedings of the National Academy of Sciences – suggests criminality is linked to impairment of neural networks involved in morality, value-based decision-making and ‘theory of mind’, the cluster of abilities for understanding the mental processes and perspectives of others. 

No impairment was shown to neural regions involved in cognitive control or empathy, the researchers report. That suggests some distinction between what makes a criminal and what makes a psychopath or sociopath, for whom lack of empathy is considered a key feature. This might explain why some psychopaths become murderous monsters – as in the case of the aforementioned serial killers – while others become successful corporate managers.

It is an “extremely interesting” result, says Winnifred Louis, a psychologist at the University of Queensland in Australia, whose research is focused on the influence of identity and norms on social decision making. 

While theory of mind – the capacity to understand other people’s point of view – is like a cognitive antecedent of empathy, Louis notes the reported absence of a connection to lower empathy highlights these criminals’ lack of victim-focus. 

“The authors suggest that what is happening in this data is that the lesions are biasing people towards more utilitarian decisions,” she says. 

Their brain impairments prevent the processing of personal moral harm to others while leaving intact utilitarian reward calculations for the self. “This is a fascinating suggestion that invites future research,” she notes.

Of the 17 individuals whose brains were mapped, 15 had no criminal record prior to their brain injuries while two showed no criminal behaviour after their brain injuries were treated. The results were supported by data from mapping the brains of 23 other criminals where there far was less definite evidence that neurological damage contributed directly to criminal behaviour. These subjects showed differently located injuries, identifiable through different sequences of MRI or CT scans, but all within a “unique connected brain network distinct from injuries not associated with criminal behaviour”.

While the findings shed light on the specific neurobiology that contributes to criminal behaviour, what makes any one person a criminal remains confoundingly complex. Factors, including genetics, upbringing and social environment, are ingredients in a murky soup. 

Edmund Kemper, for example, had already murdered his grandparents years before his motorcycle accident. The brain of Ted Bundy, another source of inspiration for Buffalo Bill, showed no sign of trauma when it was removed and examined after his execution. Previous research shows only a minority of patients suffering brain injuries associated with the network identified by this research commit crimes, while only a fifth of 239 mass-murderers in a 2014 study had a definite or suspected head injury. 

“Our work can suggest these lesions increase the likelihood of criminal behaviour,” Darby agrees,  “but we do not know the extent to which that happens, as many patients with lesions in these areas do not commit crimes.”

The results certainly help to explain why attempts to identify a specific “criminal behaviour” part of the brain have proven unsuccessful, says clinical neuropsychologist Fiona Kumfor, of Australia’s  University of Sydney, whose own research focus is on frontotemporal dementia (which studies have linked to some form of criminal behaviour in a quarter to half of all cases). “There are likely other factors we still don’t understand that causes people to behave in this way,” she says. 

One weaknesses of the study, Kumfor says, is it being based on patients, all previously published in scientific literature, who had undergone different cognitive assessments and neuroimaging. “Thus, the evidence for these abilities being involved comes from the brain network neuroimaging analysis only,” she notes. “It will be important for future studies to examine these potential functional brain networks and their associated abilities prospectively.”