There is also strong evidence that psychopaths tend to stay focused on a task - they can't or don't stop despite signals and cues from the environment that other people would find hard to ignore. Those skills may make them capable, if callous, CEOs. In the extreme cases, it may make them heartless to the pleading cries of their murder victims.
While Dr. Kiehl does his work in prisons, Dr. Gao and her colleagues recruited volunteers for some of their brain imaging studies from temporary employment agencies in Los Angeles. They found more of them had been in jail compared to the general population and some scored high on measures of psychopathic personality traits, reporting that they had done things such as running over someone in their car because they were mad at them.
"There are plenty of perfectly normal people in temp agencies - our goal was to get a good range of people then to correlate brain imaging results with measures of psychopathic personality," says Dr. Gao's colleague Andrea Glenn, a doctoral student at the University of Pennsylvania.
Ms. Glenn is interested in the genetic factors that appear to play an important role in psychopathy. "I think the main thing that we know is that psychopathic traits are moderately to highly heritable," she says. A number of candidate genes have been identified, but a large number of genes likely influence the condition.
"By identifying some of them we may be able to understand which individuals have which factors, and may be able to tailor treatments to a given individual's biology."
But first, researchers also need to understand how those genes are linked to brain deficits that have been documented in psychopathy and the role environmental factors play.
The theory is that neglect, abuse and early trauma somehow desensitize children to the feelings of others, says Dr. Kiehl, but it still has not been proven. Not all psychopaths had horrible childhoods. Some come from stable families. Millions of children are abused he says, but don't become psychopaths.
In one of her studies, Dr. Gao found that children who lived apart from their parents in the first three years of life were more likely to have psychopathic personalities. This suggests that failure to bond may play a role, she says. She also found that adults who reported they were neglected by their mothers when they were children were also more likely to have difficulty with empathy, and other psychopathic traits.
But every child showing signs of callousness and fearlessness isn't a psychopath in the making - although it certainly increases the odds. It is rare for people to become callous and unfeeling as adults if they began life as caring, empathetic children, says Paul Frick, a psychologist at the University of New Orleans, who studies anti-social behaviour and develops therapies for anti-social children. These troubled kids learn to conform quickly, often even fooling researchers by posing as model citizens until the end of the day, when, denied a reward, they become nasty intimidators even with adults.
But one study that followed 12-year-olds with these traits into adulthood found that only about 20 per cent met the measurement for psychopathy. Genes may lay the foundation, but environment builds upon it. A fearless child with callous traits who lives in a stable, supportive home with a parents that can afford to send him skiing as an outlet for his risk-taking has better outcomes than one raised in a poor family where the parents have few resources.
In the past, it was argued that psychopaths could not be treated - therapy sessions appeared to have no impact on their recidivism rates, and they often emerged having learned new skills about human nature that made them better manipulators. Some new research, however, has shown progress in teaching empathy to young children, as well as the benefits of very intense therapy for adult criminals.