Violent psychopaths cannot understand punishment because of brain abnormalities, a study has suggested.

By using MRI scans of psychopathic violent offenders, researchers found reductions in gray matter in the area of the brain that processes emotions like guilt and embarrassment. Abnormalities in white matter fiber tracts associated with lack of empathy were also found.

These parts of the brain are involved in learning from rewards and punishment.

About one in five violent offenders is a psychopath and they have higher rates of re-offending and do not appear to benefit from rehabilitation programmes.

Nigel Blackwood, from Kings College London, said: "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 now accumulating to show that both types of offenders present abnormal, but distinctive, brain development from a young age."

The researchers examined offenders convicted of murder, rape, attempted murder and grievous bodily harm. Twelve were psychopaths, 20 had antisocial personality disorders, but not psychopathy, and there were 18 healthy non-offenders.

Participants were placed in the scanner and asked to complete a task that assessed their ability to adjust their behaviour when the consequences of their responses turned from positive to negative.

It was an image matching game – sometimes points were given for getting pairs, sometimes they were not: "When these violent offenders completed neuropsychological tasks, they failed to learn from punishment cues, to change their behaviour in the face of changing contingencies, and made poorer quality decisions despite longer periods of deliberation," Blackwood said.

After looking at the brain activity, researchers found psychopaths displayed an abnormal response to punishment in posterior cingulate and insula.

"Our previous research had shown abnormalities in the white matter tract connecting these two regions. In contrast, the violent offenders without psychopathy showed brain functioning similar to that of the non-offenders," Blackwood said. "These results suggest the violent offenders with psychopathy are characterised by a distinctive organisation of the brain network that is used to learn from punishment and from rewards."

Professor Hodgins of the University of Montreal and Institut Universitaire en Santé Mentale de Montréal, said offenders with psychopathy appear only to consider the possible positive consequences of actions and do not take the negative consequences into account.

"Punishment signals the necessity to change behaviour. Clearly, in certain situations, offenders have difficulty learning from punishment to change their behaviour."

Researchers say their findings could be used to design programmes to help prevent criminality and re-offending amongst offenders with psychopathy

"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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