The study looked at 121 inmates at a medium-security prison in the United States. It divided them into groups of highly, moderately, and weakly psychopathic inmates.
(About 23% of inmates are psychopathic compared to 1% of the general population, according to that study.)
Researchers then scanned the inmates' brains, showed them images of somebody getting hurt, and asked them to imagine another human being experiencing that agony.
Brain areas tied with empathy - the anterior insula, the anterior midcingulate cortex, the somatosensory cortex, and the right amygdala - were activated when less psychopathic inmates imagined others in pain. Not so much for the highly psychopathic inmates.
While this group of inmates had a higher proportion of psychopaths than, say, your office, there are still some psychopaths mingling with the general population, some experts say. British journalist Jon Ronson, who wrote "The Psychopath Test: A Journey Through the Madness Industry," has explored the qualities shared by these psychopaths in our midst.
Armed with psychologist Robert Hare's widely used psychopath diagnostic tool, the Psychopathy Checklist-Revised (PCL-R), Ronson explored the world of mental health and criminal profiling to understand what makes some people psychopaths.
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