A Larger Striatal Volume is Associated with Increased Adult Psychopathy

Neuroscientists have identified a distinct and measurable brain difference between individuals exhibiting psychopathic traits and those with few or none, according to a groundbreaking study published in the Journal of Psychiatric Research. The research, a collaborative effort by scientists from Nanyang Technological University, Singapore (NTU Singapore), the University of Pennsylvania, and California State University, pinpointed a specific brain region involved in reward processing and motivation that demonstrates a larger volume in individuals with psychopathic tendencies. This discovery offers a significant step forward in understanding the neurobiological underpinnings of antisocial behavior.

Unveiling the Striatum: A Key to Reward and Motivation

The study employed magnetic resonance imaging (MRI) to meticulously examine the brain structures of participants. The findings revealed that the striatum, a crucial area situated deep within the forebrain, was approximately 10 percent larger on average in individuals diagnosed with psychopathic traits when compared to a control group. The striatum’s multifaceted role in brain function includes not only the planning of movements and decision-making but also the intricate processes of motivation, reinforcement learning, and the brain’s fundamental response to rewards.

Psychopathy, as a clinical construct, is generally characterized by an egocentric and antisocial personality pattern. Individuals who score high on measures of psychopathy often display a marked reduction in empathy, a diminished capacity for remorse regarding their actions, and, in a significant number of cases, an increased propensity for criminal behavior. It is critical to note that not all individuals with psychopathic traits engage in criminal activities, nor does every person who commits a crime necessarily possess psychopathic characteristics. However, a substantial body of research has consistently established a correlation between psychopathy and a heightened risk of engaging in violent behavior.

A Deeper Look at the Brain’s Reward System

Prior research had already suggested that the striatum might exhibit unusual levels of activity in individuals with psychopathy. However, the question of whether the physical size of this brain region was also implicated remained less clear. The findings published in the Journal of Psychiatric Research provide compelling evidence that psychopathy is not solely shaped by social and environmental influences, but that biological factors, such as the structural characteristics of the brain, likely play a significant role.

To rigorously investigate this potential link, the research team conducted brain scans on 120 individuals residing in the United States. These participants were also subjected to in-depth interviews utilizing the Psychopathy Checklist—Revised (PCL-R), a widely recognized and validated psychological assessment tool specifically designed to quantify psychopathic traits. The PCL-R assesses a range of characteristics, including interpersonal deficits, affective deficits, lifestyle and behavioral problems.

Assistant Professor Olivia Choy, a neurocriminologist from NTU’s School of Social Sciences and a co-author of the study, emphasized the significance of these findings. "Our study’s results help advance our knowledge about what underlies antisocial behavior such as psychopathy," she stated. "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." This statement underscores the growing recognition of the interplay between nature and nurture in the development of complex behavioral patterns.

The implications of these findings extend to a better understanding of how biological predispositions contribute to antisocial and, in some instances, criminal behavior. Over time, this enhanced knowledge could lead to the refinement of existing behavioral theories and inform the development of more effective strategies for policy-making, prevention programs, and therapeutic interventions.

The Striatum’s Role in Risk and Reward Perception

The striatum is an integral component of the basal ganglia, a collection of neuron clusters located deep within the brain. The basal ganglia serve as a critical relay station, receiving extensive input from the cerebral cortex, which governs higher-level cognitive functions such as thinking, social behavior, and the ability to selectively attend to sensory information.

Over the past two decades, the scientific community has increasingly recognized that the striatum’s influence extends beyond motor control and reward processing. Emerging evidence suggests a strong connection between the striatum and social behavior, as well as potential difficulties in social functioning.

By meticulously comparing the MRI scans with the results of the psychopathy assessments, the researchers discovered a direct correlation between a larger striatal volume and an amplified need for stimulation. This increased need for stimulation manifests as a greater inclination towards thrill-seeking, excitement, and impulsive behavior. The published study indicated that these traits of stimulation-seeking and impulsivity partially accounted for the observed relationship between striatal volume and psychopathy, explaining approximately 49.4 percent of this association.

Professor Adrian Raine, a distinguished figure in the fields of criminology, psychiatry, and psychology at the University of Pennsylvania, and another co-author of the study, highlighted the implications for developmental perspectives on psychopathy. "Because biological traits, such as the size of one’s striatum, can be inherited from parent to child, these findings give added support to neurodevelopmental perspectives of psychopathy—that the brains of these offenders do not develop normally throughout childhood and adolescence," he explained. This suggests that genetic predispositions may influence brain development, potentially leading to structural differences that contribute to psychopathic traits.

Examining Psychopathic Traits Beyond Clinical Settings

A particularly noteworthy aspect of this research was its inclusion of participants from the general community, rather than focusing exclusively on incarcerated populations. This methodological approach allowed the researchers to investigate psychopathic traits within a broader and more diverse group of individuals, providing a more representative picture of these characteristics.

Professor Robert Schug, from the School of Criminology, Criminal Justice, and Emergency Management at California State University, Long Beach, and a co-author of the study, emphasized the novelty of this approach. "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," he remarked. This broader perspective is crucial for understanding the prevalence and impact of psychopathic traits in society at large.

Exploring Gender Differences in Brain Structure

The study also included an examination of 12 women within the sample. For the first time, the research reported a link between psychopathy and an enlarged striatum in adult females, mirroring the findings in males. While acknowledging the small size of the female sample, which necessitates further investigation, this preliminary finding suggests that the observed brain pattern may not be exclusive to men. This opens up new avenues for research into potential sex-based differences and similarities in the neurobiological correlates of psychopathy.

A critical observation relates to typical human brain development, where the striatum tends to shrink as a child matures. This developmental trajectory raises the intriguing possibility that psychopathy may be connected to atypical patterns of brain development that occur across childhood and adolescence. Understanding these developmental nuances is paramount to unraveling the origins of psychopathic traits.

The Interplay of Brain Development and Environment

Assistant Professor Choy further elaborated on the need for continued research into striatal development. "A better understanding of the striatum’s development is still needed," she stated. "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." This highlights the complex, bidirectional relationship between genetics, brain development, and environmental influences.

Professor Raine reiterated the long-standing observation of reward-seeking behavior in individuals with psychopathy. "We have always known that psychopaths go to extreme lengths to seek out rewards, including criminal activities that involve property, sex, and drugs," he noted. "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." This connects the behavioral manifestations of psychopathy directly to the identified neurobiological difference.

The original study, titled "Larger striatal volume is associated with increased adult psychopathy," was formally published in the Journal of Psychiatric Research, contributing a significant piece to the complex puzzle of psychopathy.

Evolving Understanding: Beyond a Single Brain Region

Since the publication of the 2022 paper, subsequent research has continued to explore the intricate relationship between psychopathy and brain structure and networks. A 2025 study published in the European Archives of Psychiatry and Clinical Neuroscience, which examined 39 adult men diagnosed with psychopathy, found that antisocial lifestyle traits were associated with reduced volumes in several brain regions. These included parts of the basal ganglia, thalamus, basal forebrain, pons, cerebellum, orbitofrontal cortex, dorsolateral-frontal cortex, and insular cortex. The researchers concluded that these findings strongly suggest disruptions in frontal-subcortical circuits that are critical for behavioral control.

Further adding to this evolving understanding, another 2025 analysis, featured in Neuroscience and Biobehavioral Reviews, synthesized findings from 38 functional neuroimaging studies on psychopathy. While individual studies often pointed to different specific brain locations, the collective findings appeared to converge on a shared functional brain network. This network involves the default mode network and various subcortical regions. The authors of this meta-analysis proposed that psychopathy might be more comprehensively understood through a network-level perspective of brain function, rather than by isolating the role of a single brain region.

Collectively, these later findings provide a more nuanced and comprehensive picture that builds upon the foundational 2022 striatum study. The enlarged striatum finding remains a crucial clue, particularly given its established role in reward processing, stimulation-seeking, and impulsivity. However, the broader scientific consensus now suggests that psychopathy likely represents a more pervasive pattern of brain differences. These differences may encompass motivation, emotional processing, impulse control, and the complex architecture of social behavior.

Associate Professor Andrea Glenn from the Department of Psychology at The University of Alabama, who was not involved in the original 2022 study, commented on its impact. "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 essential for cognitive and social functioning," she stated. "Future studies will be needed to understand the factors that may contribute to these structural differences." This highlights the ongoing need for research to elucidate the causal pathways and developmental trajectories involved.

Scientists are actively continuing their work to understand precisely why the striatum may be enlarged in individuals with psychopathic traits. Future research endeavors are expected to shed further light on how the complex interplay of genetic predispositions, developmental processes, life experiences, and environmental factors collectively shape the brain systems that underpin reward-seeking behaviors, impulse control, and the manifestation of antisocial conduct. This ongoing scientific exploration holds the promise of leading to more targeted and effective interventions for individuals exhibiting psychopathic traits.