Nature: Brain imaging links reward system with psychopathic traits
Normal individuals who scored high on a measure of impulsive/antisocial traits display a hypersensitive brain reward system, according to a neuroradiology study published online March 14 in the journal Nature Neuroscience.

Since psychopathic individuals are at increased risk for developing substance use problems, Joshua Buckholtz, PhD candidate in neuroscience at Vanderbilt University in Nashville, Tenn., and colleagues investigated possible links between the brain’s reward system (activated by abused substances and natural reward), and a behavioral trait (impulsive/antisociality) characteristic of psychopathy.

In the study, 30 subjects had both 18F-fallypride PET and psychopathic personality inventory data (15 male, 15 female) of which 24 subjects had both blood oxygen level–dependent functional MRI  (fMRI) and psychopathic personality inventory data (8 male, 16 female). Of these 24 fMRI subjects, 10 also completed PET scans, while the remaining 14 were scanned with fMRI only.

The results in both cases showed that individuals who scored high on a personality assessment that measured traits like egocentricity, manipulating others, and risk taking had a hypersensitive dopamine response system suggesting that alterations in the function of the brain’s reward system may contribute to a latent psychopathic trait.

"The amount of dopamine released was up to four times higher in people with high levels of these traits, compared to those who scored lower on the personality profile," said Buckholtz.

Buckholtz and colleagues speculate that a heightened response to an anticipated reward could make such individuals less fearful about the consequences of their behavior, which, combined with a reduced sensitivity to others' emotions and resistance to learning from mistakes, could lead to the manipulative and aggressive style of behaviors that is common in psychopaths.

The Vanderbilt researchers hope to validate their findings with new studies on individuals who have been actually diagnosed as 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 Nora D. Volkow, MD, director of the National Institute on Drug Abuse in Washington, D.C. "However, while having an antisocial trait may be a driving factor, it is clearly not sufficient to trigger aggressive behaviors; thus, we need to continue to investigate the other contributors to psychopathy."