Psychopaths have a larger striatum region in the brain

Neuroscientists from Nanyang Technological University, Singapore (NTU Singapore), the University of Pennsylvania and California State University have established a biological difference between psychopaths and non-psychopaths, finding that a region of the forebrain known as the striatum was on average 10% larger in psychopathic individuals compared to a control group of individuals. Their work was published in the Journal of Psychiatric Research.

Psychopaths, or those with psychopathic traits, are generally defined as individuals who 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 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.

The striatum — a part of 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. In the past two decades our understanding of the striatum has expanded, yielding hints that the region is linked to difficulties in social behaviour; but while previous studies have pointed to an overly active striatum in psychopaths, they have not conclusively determined the impact of its size on behaviours.

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. Through analyses of the MRI scans and interview results, the researchers linked a larger striatum to an increased need for stimulation, through thrills and excitement, and a higher likelihood of impulsive behaviours. This was the case in females as well as males.

“We have always known that psychopaths go to extreme lengths to seek out rewards, including criminal activities that involve property, sex and drugs,” said study co-author Professor Adrian Raine, from the University of Pennsylvania. “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.”

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. Raine 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.”

Study co-author Assistant Professor Olivia Choy, from NTU, acknowledged that a better understanding of the striatum’s development is still needed. The scientists hope to carry out further research to find out the causes of the enlargement of the striatum in individuals with psychopathic traits.

“Many factors are likely involved in why one individual is more likely to have psychopathic traits than another individual,” Choy said. “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.”

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