Psychopaths lack basic hard-wiring in the brain that enables most people to be compassionate and caring, a new US study conducted on prisoners has found.
"A marked lack of empathy is a hallmark characteristic of individuals with psychopathy," said Professor Jean Decety, lead author of the study, from the University of Chicago and the University of New Mexico.
Relative to non-psychopathic criminals, psychopaths are responsible for a disproportionate amount of repetitive crime and violence in society, researchers said.
"This is the first time that neural processes associated with empathic processing have been directly examined in individuals with psychopathy, especially in response to the perception of other people in pain or distress," Decety added.
The results of the study, which could help clinical psychologists design better treatment programmes for psychopaths, are published in the journal JAMA Psychiatry.
Researchers tested 80 prisoners between ages 18 and 50 at a correctional facility. The men volunteered for the test and were tested for levels of psychopathy using standard measures.
They were then studied with functional MRI technology, to determine their responses to a series of scenarios depicting people being intentionally hurt.
They were also tested on their responses to seeing short videos of facial expressions showing pain.
The participants in the high psychopathy group exhibited significantly less activation in the ventromedial prefrontal cortex, lateral orbitofrontal cortex, amygdala and periaqueductal gray parts of the brain, but more activity in the striatum and the insula when compared to control participants, the study found.
The high response in the insula in psychopaths was an unexpected finding, as this region is critically involved in emotion and somatic resonance.
Conversely, the diminished response in the ventromedial prefrontal cortex and amygdala is consistent with the affective neuroscience literature on psychopathy.
This latter region is important for monitoring ongoing behaviour, estimating consequences and incorporating emotional learning into moral decision-making, and plays a fundamental role in empathic concern and valuing the well-being of others.
"The neural response to distress of others such as pain is thought to reflect an aversive response in the observer that may act as a trigger to inhibit aggression or prompt motivation to help," researchers said.
