Scientists Discover a Key Biological Difference Between Psychopaths and Normal People

Psychopaths have a 10% larger striatum than non-psychopaths, suggesting biological differences in brain structure. This enlargement is tied to impulsivity and a higher craving for stimulation.

The discovery, seen in both men and women, points to psychopathy’s roots in neurodevelopment. It could lead to better understanding and interventions for antisocial behavior.

Brain Scans Reveal Key Difference in Psychopaths

A team of neuroscientists from Nanyang Technological University (NTU Singapore), the University of Pennsylvania, and California State University has uncovered a biological difference between psychopaths and non-psychopaths. Using magnetic resonance imaging (MRI) scans, they found that the striatum, a region in the forebrain, was about 10% larger in individuals with psychopathic traits compared to people with little or no such tendencies.

Psychopaths, or individuals who display psychopathic traits, tend to show a combination of self-centeredness, emotional coldness, and a lack of empathy or remorse. In some cases, these characteristics are accompanied by antisocial or criminal behavior.

The striatum, part of the brain’s subcortical forebrain region, is involved in functions such as motivation, decision-making, and reward processing. It also helps coordinate motor actions and plays a role in how people plan and respond to stimuli.

The Striatum’s Role in Psychopathic Behavior

Previous studies have suggested that psychopaths may have an overactive striatum, but the effect of its size on behavior had not been confirmed until now. The new research provides evidence of a measurable biological distinction between people with and without psychopathic tendencies.

While not every person with psychopathic traits engages in crime, and not every criminal meets the definition of a psychopath, the two groups show considerable overlap. Research has also consistently linked psychopathy to aggressive and impulsive behavior.

To better understand these biological factors, researchers examined MRI scans of 120 adults in the United States. Participants were also evaluated using the Psychopathy Checklist-Revised, a standard tool for identifying psychopathic characteristics.

Assistant Professor Olivia Choy, a neurocriminologist from NTU’s School of Social Sciences and co-author of the study, explained, “Our study’s results help advance our knowledge about what underlies antisocial behavior 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.”

A Developmental and Genetic Perspective

Professor Adrian Raine from the Departments of Criminology, Psychiatry, and Psychology at the University of Pennsylvania, who co-authored the study, stated “Because biological traits, such as the size of one’s striatum, can be inherited to a child from a 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, added “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, stated “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 in the Journal of Psychiatric Research.

Bigger Striatum, Greater Need for Stimulation

The analysis of MRI scans and interview data revealed that people with larger striatums were more likely to exhibit impulsivity and a stronger desire for excitement or risk-taking behavior.

The striatum is part of the basal ganglia, a cluster of neurons located deep within the brain. The basal ganglia receive input from the cerebral cortex, which governs reasoning, social behavior, and decision-making about which sensory information deserves attention.

Over the past two decades, scientists have expanded their understanding of the striatum’s role, finding that it may also be linked to social and behavioral regulation. However, until now, few studies had examined whether these structural differences appeared in women as well as men.

Brain Differences Found in Both Men and Women

Within their group of 120 participants, the researchers identified 12 women and found, for the first time, that enlarged striatums were associated with psychopathic traits in both males and females. Normally, the striatum shrinks as the brain matures from childhood into adulthood, suggesting that psychopathy could be tied to differences in brain development.

Asst Prof Choy suggested “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 behavior in the form of enlargement to the striatum, a key brain area involved in rewards.

The research team plans to continue investigating why some individuals develop this enlargement of the striatum and how it contributes to psychopathic traits.

Reference: “Larger striatal volume is associated with increased adult psychopathy” by Olivia Choy, Adrian Raine and Robert Schug, 6 March 2022, Journal of Psychiatric Research.
DOI: 10.1016/j.jpsychires.2022.03.006

A version of this article was originally published in June 2022.

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