Psycopaths are estimated to make up 1 percent of the population and up to 25 percent of male offenders in federal correctional settings.

Differences in psychopaths' brains may help explain their anti-social behavior, according to new research.

Psychopaths are identified as highly selfish, and lacking in emotion and conscience. Experts estimate that about 1 percent of the general population and as many as 25 percent of male offenders in federal correctional settings are psychopaths. Research looking into the minds of psychopaths has found not only differences in their brains but also, at least in one recent study, speech patterns.

In the new study, which relied on scans of the brains of psychopaths incarcerated in Wisconsin, the researchers found reduced connections between a part of the brain associated with empathy and decision-making, known as the ventromedial prefrontal cortex (vmPFC), and other parts of the brain.

Using two different types of images, the researchers compared the brains of male prisoners diagnosed as psychopaths with those of prisoners who did not receive this diagnosis. Among the psychopathic prisoners, the researchers found weaker connections between the vmPFC and other parts of the brain, including the amygdala.

The amygdala itself is associated with emotion, memory and fear. Interactions between the vmPFC and the amygdala are believed to underlie aspects of emotion regulation, aggression and stimulus reinforced associations, the researchers write in an article published in the most recent issue of the Journal of Neuroscience.

"Those two structures in the brain, which are believed to regulate emotion and social behavior, seem to not be communicating as they should," said Michael Koenigs, a study researcher and assistant professor of psychiatry at the University of Wisconsin School of Medicine and Public Health.

This study builds on previous work in which Koenigs and colleague Joseph Newman, a psychology professor at University of Wisconsin-Madison, showed that psychopaths responded to decision-making tests in a manner resembling that of patients who had suffered damage to their vmPFC.

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