Psychopaths are usually described as lacking empathy, and a new study reveals the neurological basis for this dearth of feeling.

When people with psychopathy imagine others experiencing pain, brain regions associated with empathy and concern for others fail to activate or connect with brain areas involved in emotional processing and decision-making, researchers report.

In addition to a lack of remorse, psychopathy is characterized by shallow affect, glibness, manipulation and callousness. The rate of psychopathy is about 23 percent in prisons, compared with about 1 percent in the general population, research shows. [The 9 Most Bizarre Medical Conditions]

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To investigate the neurological roots of the disorder, researchers studied 121 inmates at a medium-security prison in the United States. The inmates were divided into highly psychopathic, moderately psychopathic and weakly psychopathic groups on the basis of a widely used diagnostic tool called the Hare Psychopathy Checklist-Revised.

Researchers scanned the brains of the participants while showing them images depicting physical pain, such as a finger getting caught in a door or a toe caught under a heavy object. The participants were told to imagine the accident happening to themselves or to someone else. They were also shown images of neutral ojects, such as a hand on a doorknob.

When the highly psychopathic individuals imagined the accidents happening to themselves, their brains lit up in the anterior insula, the anterior midcingulate cortex, the somatosensory cortex and the right amygdala — all areas involved in empathy. The response was quite pronounced, suggesting psychopathic individuals were sensitive to thoughts of pain.

But when the highly psychopathic inmates imagined the accident happening to others, their brains failed to light up in the regions associated with empathy. In fact, an area involved in pleasure, the ventral striatum, lit up instead. Furthermore, these individuals showed abnormal connectivity between the insula and the ventromedial prefrontal cortex, an area important for empathetic decision-making.

By contrast, the less psychopathic individuals showed more normal brain activation and connectivity in these areas.

The strange patterns of brain activation and connectivity in highly psychopathic individuals suggest they did not experience empathy when imagining the pain of others, and possibly took pleasure in it.

The findings could help inform intervention programs for psychopathy, the researchers say. Having psychopathic people imagine themselves in pain first could be used in cognitive behavior therapies as a way of kick-starting empathy, they wrote in the study detailed today (Sept. 24) in the journal Frontiers in Human Neuroscience.

In fact, past research has shown psychopaths can feel empathy, when explicitly asked to, suggesting this ability to understand another person's feelings may be repressed rather than missing entirely in psychopathic individuals.

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