Brain scans reveal a shocking difference between psychopaths and other people

Using magnetic resonance imaging (MRI), the team found that the striatum was about 10 percent larger on average in psychopathic individuals compared with a control group. The striatum sits deep in the forebrain and plays a role in movement planning, decision-making, motivation, reinforcement, and how the brain responds to rewards.

Psychopathy is generally associated with an egocentric and antisocial personality pattern. People with strong psychopathic traits often show reduced empathy, little remorse for harmful actions, and, in some cases, a greater likelihood of criminal behavior. Not everyone with psychopathic traits commits crimes, and not every person who commits a crime is a psychopath, but research has consistently linked psychopathy with a higher risk of violent behavior.

A Larger Reward Center in the Brain

Earlier research had suggested that the striatum may be unusually active in psychopaths, but it was less clear whether the size of this brain region was also involved. The Journal of Psychiatric Research findings added evidence that psychopathy is not shaped only by social and environmental experiences. Biology may also play a role.

To investigate the link, the researchers scanned the brains of 120 people in the United States. They also interviewed the participants using the Psychopathy Checklist -- Revised, a widely used psychological assessment designed to measure psychopathic traits.

Assistant Professor Olivia Choy, from NTU's School of Social Sciences, a neurocriminologist who co-authored the study, said: "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."

The findings may help researchers better understand how biology contributes to antisocial and criminal behavior. Over time, that knowledge could help refine theories of behavior and inform future approaches to policy, prevention, and treatment.

What the Striatum May Reveal About Risk and Reward

The striatum is part of the basal ganglia, a group of neuron clusters located deep in the brain. The basal ganglia receive information from the cerebral cortex, which helps control thinking, social behavior, and the ability to decide which sensory information deserves attention.

Over the past two decades, scientists have increasingly recognized that the striatum is not only involved in movement and reward. It may also be tied to social behavior and difficulties in social functioning.

By comparing MRI scans with psychopathy assessment results, the researchers found that a larger striatum was linked to a stronger need for stimulation, including thrill-seeking, excitement, and impulsive behavior. In the published study, stimulation-seeking and impulsivity partly explained the relationship between striatal volume and psychopathy, accounting for 49.4 percent of the association.

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."

Psychopathic Traits Outside Prison Populations

One important feature of the study was that it included people from the community rather than focusing only on prison populations. That helped the researchers examine psychopathic traits in a broader group of individuals.

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."

The researchers also examined 12 women in the study sample. They reported that, for the first time, psychopathy was linked to an enlarged striatum in adult females as well as males. The female sample was small, so the finding needs further study, but it suggested that the same brain pattern may not be limited to men.

In typical human development, the striatum tends to shrink as a child matures. That pattern raises the possibility that psychopathy may be connected to differences in brain development across childhood and adolescence.

Brain Development and Environment May Both Matter

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 behavior in the form of enlargement to the striatum, a key brain area involved in rewards."

The study was published in the Journal of Psychiatric Research under the title "Larger striatal volume is associated with increased adult psychopathy."

Later Research Points to a Wider Brain Network

Since the 2022 paper, later research has continued to explore how psychopathy relates to brain structure and brain networks. A 2025 study in European Archives of Psychiatry and Clinical Neuroscience examined 39 adult men diagnosed with psychopathy and found that antisocial lifestyle traits were associated with reduced volumes in several brain regions, including parts of the basal ganglia, thalamus, basal forebrain, pons, cerebellum, orbitofrontal cortex, dorsolateral-frontal cortex, and insular cortex. The researchers concluded that these findings point to disruptions in frontal-subcortical circuits involved in behavioral control.

Another 2025 analysis in Neuroscience and Biobehavioral Reviews looked across 38 functional neuroimaging studies of psychopathy. Although individual studies often pointed to different brain locations, the findings appeared to map onto a shared functional brain network involving the default mode network and subcortical regions. The authors argued that psychopathy may be better understood through a network-level view of the brain rather than by focusing on one region alone.

Together, these later findings add nuance to the 2022 striatum study. The enlarged striatum finding remains an important clue, especially because of the striatum's role in reward, stimulation, and impulsivity. However, psychopathy likely reflects a broader pattern of brain differences involving motivation, emotional processing, impulse control, and social behavior.

Associate Professor Andrea Glenn from the Department of Psychology of The University of Alabama, who was not involved in the 2022 study, 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."

Scientists are still working to understand why the striatum may be enlarged in people with psychopathic traits. Future work may help clarify how genetics, development, life experiences, and environment interact to shape the brain systems involved in reward-seeking, impulse control, and antisocial behavior.