Amnesty International supporters wearing orange boiler suits hold a night long vigil in a cage against Guantanamo Bay detentions. Daniel Berehulak/Getty Images

Violent psychopaths have abnormalities in the parts of the brain related to learning from punishment, according to research reported in the British journal Lancet Psychiatry.

Scientists say psychopaths have remained unaffected by punishment since childhood, suggesting rehabilitation programs probably won’t work.

One in five violent offenders is a psychopath. They keep offending and they don’t benefit from rehabilitation.

“Our research reveals why this is and can hopefully improve childhood interventions to prevent violence and behavioural therapies to reduce recidivism,” says Professor Sheilagh Hodgins of the University of Montreal.

“Psychopathic offenders are different from regular criminals in many ways. Regular criminals are hyper-responsive to threat, quick-tempered and aggressive, while psychopaths have a very low response to threats, are cold, and their aggression is premeditated.”

Evidence is accumulating to show that psychopaths have abnormal and distinctive brain development from a young age.

Using Magnetic Resonance Imaging, the researchers found structural abnormalities in the brains of the violent offenders, some convicted of murder, rape, attempted murder and grevious bodily harm.

“In childhood, both psychopathic and non-psychopathic offenders alike are repeatedly punished by parents and teachers for breaking rules and for assaulting others, and from adolescence onwards, they are frequently incarcerated,” Hodgins said. “Yet they persist in engaging in violent behaviour towards others. Thus, punishment does not appear to modify their behaviour.”

The research is critical to the development of programs to prevent violent criminality.

“Since most violent crimes are committed by men who display conduct problems from a young age, learning-based interventions that target the specific brain mechanisms underlying this behaviour pattern and thereby change the behaviour would significantly reduce violent crime,” Hodgins said.

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