The amygdala is the area of the brain where people process emotions. In psychopaths, this area is up to 18% smaller. When most people are given a moral dilemma to consider, such as the trolley problem, the amygdala fires up and lights up on brain scans. In psychopaths, this doesn't happen to the same degree.
"We know that there are strong genetic contributions to the brain areas, but we also know that the social environment can impact the brain," Raine said. "People who are abused early in life or who are neglected, for example, they have a reduction in the volume of the amygdala. That's at least true in children. So it can be genes and it can be the environment. Most likely, it's a combination of both."
Surprisingly, in the new study, the psychopathic offenders' pupils responded normally to positive images like happy couples and animals, which suggests psychopathy may not be associated with a complete lack of emotions, but a reduced sensitivity to threatening information.
Their pupils also dilated when seeing smiling faces, which the authors suggest could be because psychopaths are sometimes suspicious of people who appear happy.
"Many psychopathic offenders appear to be bold, confident, and can act in cold-blooded manner," said Robert Snowden from Cardiff University. "It's much easier to act bold if you have no feelings of fear, and to be cold-blooded if there is no emotion to get in the way of the act."
