Researchers have found evidence of brain abnormalities in psychopaths convicted of violent offences, including murder, rape and grievous bodily harm.
The UK study, carried out by London's King's College, used magnetic resonance imaging (MRI) scans to measure the volume of grey matter in violent men's brains.
Psychopaths were found to have structural differences in parts of the brain responsible for understanding emotions compared to other violent offenders and non-offenders.
The study, published online this week in the Archives of General Psychiatry, scanned the brains of 66 men, including 17 psychopaths with antisocial personality disorder (ASPD).
Twenty-seven men who were not psychopaths but had ASPD and 22 healthy non-offenders also had MRI scans.
The psychopaths had less grey matter in the anterior rostral prefrontal cortex and temporal poles of the brain when compared with other violent offenders and the healthy men.
These areas of the brain are important for processing emotions, fear, and social skills.
"These brain regions are thus central to the development of self-conscious emotions, such as guilt or embarrassment, which promote prosocial behaviour and form the basis of moral learning," lead author Nigel Blackwood said.
He said the reduced volume of grey matter could contribute to the profound social impairments that characterise psychopathy.
Mr Blackwood said while the basic empathy processing appeared to be intact in this group, emotional aspects were impaired, with diminished responses to fear and distress in others.
"Men with the syndrome of psychopathy fail to learn from their experience of punishment and to experience self-conscious emotions such as guilt, remorse, or embarrassment, which facilitate desistance from the use of inappropriate behaviours, most significantly aggression and violence," he said.
Mr Blackwood said the results had important implications for treatment options.