Posted by Phillipa on March 23, 2010, at 19:54:21
Reward systems of psychopaths may be fueled by an excess of dopamine. Phillipa
Psychopaths Programmed to Be Reward Seekers
Jill Stein
Psychopaths doggedly pursue rewards without particular concern about potential consequences, and this tendency seems to be due to a malfunctioning brain reward system, new data suggest.Published online March 14 in Nature Neuroscience, the findings were reported by investigators from Vanderbilt University, Nashville, Tennessee.
"The heightened dopamine release we found in the brains of individuals with psychopathic traits suggests that psychopathy may reflect dysfunction in dopamine reward circuitry," lead author Joshua W. Buckholtz, BS, who is studying for his doctoral degree in neuroscience, told Medscape Psychiatry.
"This study identifies a new brain system as being involved in psychopathy and may lead the way for future studies that target this system as a way of reducing aggression and antisocial behavior," he said.
"It also sheds light on the fact that, despite the availability of good evidence for underreactivity to some kinds of emotional stimuli, psychopaths don't have a general lack of emotional reactivity," he added.
"In fact, the observed overreactivity of dopamine might cause them to pay more attention to obtaining rewards (like money, sex, or status) at the cost of attending to other things, like the potential consequences of their actions to their victims or even themselves," said Mr. Buckholtz.
Lack of Information
Psychopathy is a personality disorder with cardinal traits that include superficial charm, antisocial behavior, sensation-seeking and impulsive behavior, a lack of empathy and sensitivity to punishment, and shallow emotional experiences. The disorder is recognized to be a strong predictor of criminal behavior and recidivism.
To date, research on the neural basis of psychopathy has mostly examined the emotional and interpersonal deficits in psychopaths, such as a lack of fear or sensitivity to punishment, and has largely ignored the disorders impulsive-antisocial components, such as manipulativeness, egocentricity, and aggression.
However, it is the disorders impulsive-antisocial traits that have been established to be most closely linked with the violent and criminal behaviors seen in psychopaths.
Prior studies have also demonstrated that psychopathic individuals have a significantly increased risk of developing substance abuse and that the dopamine system is involved in the pathophysiology of substance abuse.
"It seemed that the next logical step was to look at whether psychopathic traits are associated with changes in dopamine reward circuitry," Mr. Buckholtz said.
For their study, the researchers explored possible associations between the brains reward system (in response to pharmacologic and monetary rewards) and the impulsivity and antisocial behavior that typifies psychopathy.
PET and fMRI Data Consistent
The team, from the laboratory of David Zald, PhD, associate professor of psychology and psychiatry, used positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) to examine the relationship between psychopathic traits and dopamine release in the nucleus accumbens (NA). The NA is known to be involved in dopamine reward processing.
Study participants, all of whom were volunteers from the community with no prior history of substance abuse, completed the Psychopathic Personality Inventory (PPI) test. This test, which is a widely validated tool for assessing the presence and severity of psychopathic traits in individuals 18 to 86 years of age, includes 2 dimensions.
The fearless dominance factor comprises the emotional and interpersonal components of psychopathy, whereas the impulsive-antisociality factor refers to the socially deviant behaviors exhibited by psychopaths. The PPI impulsive-antisociality subscale has been found to be associated with aggression, impulsivity, and substance abuse in the prison population and the community at large.
In the first part of the study, the team used PET to measure dopamine release in the brain in 30 volunteers who had been given low-dose oral amphetamine (0.43 mg/kg of body weight).
Results showed a strong correlation between scores on the PPIs impulsive-antisociality subscale and amphetamine-induced dopamine release in bilateral NA. In fact, individuals with high scores on the impulsive-antisociality subscale had nearly 4 times the amount of dopamine release in bilateral NA in response to the amphetamine as individuals with low levels of psychopathic traits.
In the second part of the study, 24 volunteers were told that they would be paid money provided they completed a single simple task. The volunteers underwent an fMRI scan while they performed the task.
The investigators had predicted that individuals with high levels of impulsive-antisocial traits would demonstrate enhanced NA recruitment as a result of monetary reinforcement. "And this is exactly what we found," Mr. Buckholtz said.
"People with high levels of these psychopathic traits showed much more brain activity in the nucleus accumbens when they were given the opportunity to make button presses to earn a cash reward."
Perhaps the most surprising study finding was the selectivity of the link between dopamine reward system function, he added. "While we found very strong associations between dopamine function and impulsive-antisocial traits, there was virtually no evidence for a link between fearless dominance traits and dopamine function," he said.
Finally, Buckholtz and his coauthors pointed out in their article that the research is the first to demonstrate that psychopathic behavioral manifestations are closely linked with changes in brain activity. As for future research, the group hopes to determine whether similar changes are seen in incarcerated psychopaths.
Clinical Relevance
"The paper is really interesting," Julian Beezhold, MBChB, FRCPsych, consultant in emergency psychiatry at Hellesdon Hospital in Norwich, United Kingdom, told Medscape Psychiatry.
"It sheds some light on the big question of why psychopaths behave the way that they do and may also eventually lead to some future medication options to help modify psychopathic behavior. Overall, the study provides a tantalizing glimpse into how basic neuroscience research may directly lead to clinical interventions," he said.
Dr. Beezhold added that the study was "carefully done and the conclusions are compelling" and added that, like all research, the findings need to be replicated by other investigators.
Future research should also examine the extent to which "the dopamine reward system functioning is governed by both nature and nurture, and this will help us determine whether there are options for early and possibly preventative treatment," he added.
The study was funded by the National Institute on Drug Abuse. The study authors and Dr. Beezhold have disclosed no relevant financial relationships.
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