Toronto - Brain researcher Daniel Tranel has discovered that social misfits have defects in a part of the brain he calls the "moral compass".
He studied many previously sociable patients who had suffered damage to grey matter in the area known as the ventromedial prefrontal cortex, above the eyeballs.
All had turned antisocial and reckless after the injury, usually from a stroke, disease, gunshot or accident.
Tranel, a neuropsychology professor at the University of Iowa, presented conclusions from his 20 years of research at an international neurology conference in Toronto this week.
In related research, Adrian Raine, a University of Southern California psychology professor, found that criminals had on average 11 percent smaller prefrontal cortex mass than normal people.
Tranel found that people with moral compass damage lost the ability to base their actions on moral reasoning and knowledge of consequences from prior experience.
"Their behaviour can become random," he said.
Last year he co-authored a study of case histories suggesting damage to the prefrontal cortex in childhood could lead to a life of crime. It prompted enquiries from lawyers.
"They said, 'Okay, if you scientists think that is the case, then are these people responsible for their actions if they are just not wired right?'."
He had declined giving an opinion, saying this was not his job. - Sapa