It is well known that psychopaths can commit violent, and often criminal, acts. But the precise neural mechanisms that underlie this behavior have remained elusive. However, new research reveals the neural circuits that may drive psychopathic behavior.
What goes on in the mind of a psychopath? From specialized neuroscientific studies to popular psychology books, this head-scratching question has preoccupied scientists, ethicists, and journalists alike for years.
While it is known that psychopaths sometimes display violent or criminal-like behavior, the neurological underpinnings of this condition have remained somewhat of a mystery.
But a team of researchers from Harvard University in Cambridge, MA - led by Joshua Buckholtz, an associate professor of psychology - recently set out to unravel some of this mystery. By examining the brain scans of almost 50 inmates in two medium-security prisons in Wisconsin, Prof. Buckholtz and his team examined what makes psychopaths act the way they do, as well as what drives their decision-making.
We may not yet know what goes on in the mind of a psychopath, but the new findings - which are published in the journal Neuron - may help us to understand what goes on their brain.
Studying psychopaths in prisons
As the authors explain, previous studies have pointed to an association between the impulsive-antisocial factor and reward-anticipating circuits in the brain, as measured by blood-oxygen-level-dependent signaling, which is a standard technique used in functional MRI.
For example, some studies have found a higher volume of striatal gray matter in teenagers with impulsive-antisocial symptoms, as well as in psychopathic offenders.
Additionally, Prof. Buckholtz and team have shown in a previous study that scoring highly on the impulsive-antisocial scale correlated strongly with dopamine-releasing circuits and increased brain activity in areas associated with reward anticipation - namely, the nucleus accumbens.
All of these studies suggested to the researchers that psychopathic behavior may be associated with excessive dopamine transmission and a stronger "functional reactivity to rewards" in the striatum. So they set out to investigate whether or not their hypothesis was correct.
As part of the study, 49 inmates were asked to complete a so-called delayed gratification test while their brains were scanned using mobile scanners. In the test, participants had to choose between receiving a small amount of money right away and being given a larger amount later on.
The researchers then estimated the subjective value that each of the two options presented to the participants. The sum of these subjective values was fed into a model based partially on studies carried out in primates.
The model enabled the scientists to measure the impulsivity of the participants' choices, as well as to detect the brain areas that are key in judging the value of these choices.
The researchers also examined the inmates' psychopathic characteristics using a traditional psychopathy test called the Hare Psychopathy Checklist-Revised.
Psychopathy as 'brain wiring dysfunction'
"[The] more psychopathic a person is, the greater the magnitude of that striatal response," Prof. Buckholtz explains. "That suggests that the way they are calculating the value rewards is dysregulated - they may over-represent the value of immediate reward."
The experiment confirmed the scientists' hypothesis. Prof. Buckholtz and team found that inmates with the highest score on the psychopathy test also showed higher activity in a brain area called the ventral striatum, a region key for assessing immediate rewards.
Normally, the activity in the brain's ventral striatum is also regulated by another brain region, called the ventral medial prefrontal cortex (vmPFC).
This area is involved in social and moral decision-making, fear learning, and empathic responses. The vmPFC is also responsible for the ability to project the consequences of our actions and decisions into the future.
Thus, the vmPFC can control how the striatum represents the value of a reward, and without this regulation, the value of that reward may be overestimated.
Prof. Buckholtz and team mapped several brain areas that were connected to the ventral striatum to see how they influence decision-making, and they found that the connectivity between the vmPFC and the ventral striatum was weakened.
"[We] found that connections between the striatum and the ventral medial prefrontal cortex were much weaker in people with psychopathy," Prof. Buckholtz explains. "If you break that connection in anyone, they're going to start making bad choices because they won't have the information that would otherwise guide their decision-making to more adaptive ends."
Importantly, the effect of weak corticostriatal connectivity was so clear that the researchers were able to predict the number of criminal convictions that the inmates had each received.
"The same kind of short-sighted, impulsive decision-making that we see in psychopathic individuals has also been noted in compulsive over-eaters and substance abusers."
"If we can put this back into the domain of rigorous scientific analysis, we can see psychopaths aren't inhuman, they're exactly what you would expect from humans who have this particular kind of brain wiring dysfunction."
Prof. Joshua Buckholtz