John Cookson at Big Think:
Is a person's propensity toward evil a matter of malfunctioning synapses and neurons?
Michael Stone, professor of clinical psychiatry at Columbia University and author of “The Anatomy of Evil,” says it is. Ever-more-detailed brain scans are revealing the biological origins of psychological issues in “evil” people, from those who are mildly antisocial to serial murderers.
Under each brain’s wrinkly cortex lies the limbic system, an evolutionary heirloom controlling emotion and motivation, among other functions. Within this limbic system is the amygdala, an almond-shaped cluster of nuclei that processes our feelings of fear and pleasure.
Murderers and other violent criminals have been shown to have amygdalae that are smaller or that don’t function properly, explains Stone. One recent study concluded that individuals who exhibit a marker of “limbic neural maldevelopment” have “significantly higher levels of antisocial personality, psychopathy, arrests and convictions compared with controls.”
The amygdala is important because, among its other functions, it allows an individual to respond to the facial expressions of others. When a person has an abnormal amygdala—one that doesn't process the facial expressions of emotion—they can have an inability to register the fear and suffering of a victim, says Stone. This lack of response to the emotions of others predisposes an individual to antisocial, even criminal, behavior.
More here.