Psychopathic individuals are more likely to have larger striatum region in the brain

Neuroscientists from Nanyang Technological University, Singapore (NTU Singapore), University of Pennsylvania, and California State University, have established the existence of a biological difference between psychopaths and non-psychopaths.

Using magnetic resonance imaging (MRI) scans, they found that a region of the forebrain known as the striatum, was on average ten per cent larger in psychopathic individuals compared to a control group of individuals that had low or no psychopathic traits.

Psychopaths, or those with psychopathic traits, are generally defined as individuals that have an egocentric and antisocial personality. This is normally marked by a lack of remorse for their actions, a lack of empathy for others, and often criminal tendencies.

The striatum, which is a part of the forebrain, the subcortical region of the brain that contains the entire cerebrum, coordinates multiple aspects of cognition, including both motor and action planning, decision-making, motivation, reinforcement, and reward perception.

Previous studies have pointed to an overly active striatum in psychopaths but have not conclusively determined the impact of its size on behaviours. The new study reveals a significant biological difference between people who have psychopathic traits and those who do not.

While not all individuals with psychopathic traits end up breaking the law, and not all criminals meet the criteria for psychopathy, there is a marked correlation. There is clear evidence that psychopathy is linked to more violent behaviour.

The understanding of the role of biology in antisocial and criminal behaviour may help improve existing theories of behaviour, as well as inform policy and treatment options.

To conduct their study, the neuroscientists scanned the brains of 120 participants in the United States and interviewed them using the Psychopathy Checklist -- Revised, a psychological assessment tool to determine the presence of psychopathic traits in individuals.

Assistant Professor Olivia Choy, from NTU's School of Social Sciences, a neurocriminologistwho co-authored the study, said: "Our study's results help advance our knowledge about what underlies antisocial behaviour such as psychopathy. We find that in addition to social environmental influences, it is important to consider that there can be differences in biology, in this case, the size of brain structures, between antisocial and non-antisocial individuals."

Professor Adrian Raine from the Departments of Criminology, Psychiatry, and Psychology at University of Pennsylvania, who co-authored the study, said: "Because biological traits, such as the size of one's striatum, can be inherited to child from parent, these findings give added support to neurodevelopmental perspectives of psychopathy -- that the brains of these offenders do not develop normally throughout childhood and adolescence."

Professor Robert Schug from the School of Criminology, Criminal Justice, and Emergency Management at California State University, Long Beach, who co-authored the study, said: "The use of the Psychopathy Checklist -- Revised in a community sample remains a novel scientific approach: Helping us understand psychopathic traits in individuals who are not in jails and prisons, but rather in those who walk among us each day."

Highlighting the significance of the work done by the joint research team, Associate Professor Andrea Glenn from the Department of Psychology of The University of Alabama, who is not involved in the research, said: "By replicating and extending prior work, this study increases our confidence that psychopathy is associated with structural differences in the striatum, a brain region that is important in a variety of processes important for cognitive and social functioning. Future studies will be needed to understand the factors that may contribute to these structural differences."

The results of the study were published recently in the peer-reviewed academic publication Journal of Psychiatric Research.

Bigger striatum, larger appetite for stimulation

Through analyses of the MRI scans and results from the interviews to screen for psychopathy, the researchers linked having a larger striatum to an increased need for stimulation, through thrills and excitement, and a higher likelihood of impulsive behaviours.

The striatum is part of the basal ganglia, which is made up of clusters of neurons deep in the centre of the brain. The basal ganglia receive signals from the cerebral cortex, which controls cognition, social behaviour, and discerning which sensory information warrants attention.

In the past two decades, however, the understanding of the striatum has expanded, yielding hints that the region is linked to difficulties in social behaviour.

Previous studies have not addressed whether striatal enlargement is observed in adult females with psychopathic traits.

The neuroscientists say that within their study of 120 individuals, they examined 12 females and observed, for the first time, that psychopathy was linked to an enlarged striatum in females, just as in males. In human development, the striatum typically becomes smaller as a child matures, suggesting that psychopathy could be related to differences in how the brain develops.

Asst Prof Choy added: "A better understanding of the striatum's development is still needed. Many factors are likely involved in why one individual is more likely to have psychopathic traits than another individual. Psychopathy can be linked to a structural abnormality in the brain that may be developmental in nature. At the same time, it is important to acknowledge that the environment can also have effects on the structure of the striatum."

Prof Raine added: "We have always known that psychopaths go to extreme lengths to seek out rewards, including criminal activities that involve property, sex, and drugs. We are now finding out a neurobiological underpinning of this impulsive and stimulating behaviour in the form of enlargement to the striatum, a key brain area involved in rewards.

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Not all psychopaths are violent; a new study may explain why some are 'successful' instead

Psychopathy is widely recognized as a risk factor for violent behavior, but many psychopathic individuals refrain from antisocial or criminal acts. Understanding what leads these psychopaths to be "successful" has been a mystery.

A new study conducted by researchers at Virginia Commonwealth University sheds light on the mechanisms underlying the formation of this "successful" phenotype.

"Psychopathic individuals are very prone to engaging in antisocial behaviors but what our findings suggest is that some may actually be better able to inhibit these impulses than others," said lead author Emily Lasko, a doctoral candidate in the Department of Psychology in the College of Humanities and Sciences. "Although we don't know exactly what precipitates this increase in conscientious impulse control over time, we do know that this does occur for individuals high in certain psychopathy traits who have been relatively more 'successful' than their peers."

The study, "What Makes a 'Successful' Psychopath? Longitudinal Trajectories of Offenders' Antisocial Behavior and Impulse Control as a Function of Psychopathy," will be published in a forthcoming issue of the journal Personality Disorders: Theory, Research, and Treatment.

When describing certain psychopathic individuals as "successful" versus "unsuccessful," the researchers are referring to life trajectories or outcomes. A "successful" psychopath, for example, might be a CEO or lawyer high in psychopathic traits, whereas an "unsuccessful" psychopath might have those same traits but is incarcerated.

The study tests a compensatory model of "successful" psychopathy, which theorizes that relatively "successful" psychopathic individuals develop greater conscientious traits that serve to inhibit their heightened antisocial impulses.

"The compensatory model posits that people higher in certain psychopathic traits (such as grandiosity and manipulation) are able to compensate for and overcome, to some extent, their antisocial impulses via increases in trait conscientiousness, specifically impulse control," Lasko said.

To test this model, the researchers studied data collected about 1,354 serious juvenile offenders who were adjudicated in court systems in Arizona and Pennsylvania.

"Although these participants are not objectively 'successful,' this was an ideal sample to test our hypotheses for two main reasons," the researchers write. "First, adolescents are in a prime developmental phase for the improvement of impulse control. Allowing us the longitudinal variability we would need to test our compensatory model. Second, offenders are prone to antisocial acts, by definition, and their rates of recidivism provided a real-world index of 'successful' versus 'unsuccessful' psychopathy phenotypes."

The study found that higher initial psychopathy was associated with steeper increases in general inhibitory control and the inhibition of aggression over time. That effect was magnified among "successful" offenders, or those who reoffended less.

Its findings lend support to the compensatory model of "successful" psychopathy, Lasko said.

"Our findings support a novel model of psychopathy that we propose, which runs contradictory to the other existing models of psychopathy in that it focuses more on the strengths or 'surpluses' associated with psychopathy rather than just deficits," she said. "Psychopathy is not a personality trait simply composed of deficits -- there are many forms that it can take."

Lasko is a researcher in VCU's Social Psychology and Neuroscience Lab, which seeks to understand why people try to harm one another. David Chester, Ph.D., director of the lab and an assistant professor of psychology, is co-author of the study.

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