People who scored high on a test that measures impulsive and antisocial traits had exaggerated brain responses to certain “rewards,” like winning money or taking stimulant drugs. The new study provides evidence that a dysfunctional brain reward system may underlie vulnerability to a personality disorder known as psychopathy.
Psychopathy is characterized by a combination of superficial charm, manipulative and antisocial behavior, impulsivity, blunted empathy and shallow emotional experiences. Psychopathy is a reliable predictor of criminal behaviour and repeat offenders. Research also suggests that psychopathic people are at increased risk for substance abuse.
Many studies of psychopathy have focused on the emotional and interpersonal aspects of the disorder, like lack of fear and empathy. But Joshua W. Buckholtz and his colleagues at Vanderbilt University decided to take a closer look at a different facet of psychopathy that’s linked to socially deviant behaviour, impulsivity, aggression and substance abuse.
In a study supported by NIH’s National Institute on Drug Abuse (NIDA), the researchers used different imaging techniques to scan the brain’s reward responses in more than 40 healthy adults, ages 18 to 35, who had no history of substance abuse. None had psychopathy, but some scored high on measures of traits associated with psychopathy.
In one experiment, the researchers used positron emission tomography (PET) to image the brain’s dopamine response when participants received a low oral dose of amphetamine. This stimulant drug is known to activate the release of dopamine, a brain chemical associated with reward and motivation.
In the second experiment, participants played a computer a game in which they could win money. Their brains were scanned using functional MRI as they anticipated their monetary rewards. The findings were reported on March 14, 2010, in the advance online edition of Nature Neuroscience.
The results in both cases show that people with higher scores for impulsive and antisocial traits had greater responses in the dopamine reward areas of the brain. In the first study, the amount of dopamine released was up to 4 times higher in those who scored high for these traits, compared to those with lower scores. In contrast, scores for the emotional and interpersonal aspects of psychopathy did not correlate with the brain's reward responses.
The researchers speculate that heightened responses to an anticipated reward could make such individuals less fearful about the consequences of their behavior. This, combined with a reduced sensitivity to others' emotions, could lead to the manipulative and aggressive behaviours common to psychopaths.
"By linking traits that suggest impulsivity and the potential for antisocial behavior to an overreactive dopamine system, this study helps explain why aggression may be as rewarding for some people as drugs are for others," said NIDA Director Dr. Nora Volkow. "However, while having an antisocial trait may be a driving factor, it is clearly not sufficient to trigger aggressive behaviours; thus, we need to continue to investigate the other contributors to psychopathy."
Source: http://www.nih.gov/
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