An overactive dopamine reward system in the brain may help explain why psychopaths pursue rewards without regard for consequences, according to new research published this week in the journal Nature Neuroscience. Previous research has found that individuals who suffer from antisocial personality disorder—often referred to as sociopathology or psychopathology, despite debate over whether these are distinct conditions—lack empathy and fear. Yet this new study, from researchers at Vanderbilt University examines what these individuals may have in excess. According to the study, led by Joshua Buckholtz, a graduate student in psychology at Vanderbilt, individuals with antisocial personality disorder traits show signs of dysfunction in dopamine reward systems—suggesting that, in psychopaths, the drive toward reward can overwhelm all else.
Prior to participating in two different experiments, study subjects completed personality tests to identify presence and severity of psychopathic characteristic—including aggression, lack of empathy, and capacity for manipulation, among other things. Drawing on previous research that has established a strong link between substance abuse and psychopathology, in the first experiment researchers gave participants amphetamine, then used functional Magentic Resonance Imaging (fMRI) brain scans to monitor how dopamine release was affected by the stimulant. In a second experiment, study participants were told that they would be paid for performing a simple task, and researchers conducted brain scans while they completed the tasks.
In both experiments, researchers found that participants who had psychopathic characteristics according to the personality test, were more likely than those without those traits to have greater activity in the nucleus accumbens, the area of the brain associated with dopamine reward processing—whether in response to the chemical stimulant, or the suggestion of monetary reward.
The findings suggest that individuals with antisocial personality disorder may not be unaware of or simply dismissive of consequences, Buckholtz indicates, but instead that their intense reward-seeking motivation consumes their attention wholly until they have fulfilled their desire for reward. These findings may shed light on the violent and criminal behavior often characteristic of psychopaths, and even open doors toward new forms of treatment.
Check out TIME’s top 25 horror movies.
Read TIME’s special cover package on the science of happiness.
