Brains of psychopaths are wired to over-value immediate rewards and neglect future consequences of their actions, making them more violent and anti-social, Harvard scientists say.
Researchers took brain scans of nearly 50 prison inmates to help explain why psychopaths make poor, dangerous decisions.
"Even though psychopaths are often portrayed as cold-blooded, almost alien predators, we have been showing that their emotional deficits may not actually be the primary driver of these bad choices," said Josh Buckholtz, from Harvard University in the US.
"Because it's the choices of psychopaths that cause so much trouble, we've been trying to understand what goes on in their brains when they make decisions that involve trade-offs between the costs and benefits of action," said Buckholtz.
Psychopaths commit an astonishing amount of crime, and this crime is both devastating to victims and astronomically costly to society as a whole.
Researchers looked at brain-based measures of reward and value and the communication between different brain regions that are involved in decision making.
They used a "mobile" scanner - typically used for cancer screenings in rural areas.
The team scanned the brains of 49 inmates over two hours as they took part in a type of delayed gratification test which asked them to choose between two options - receive a smaller amount of money immediately, or a larger amount at a later time.
The results of those tests were then fit to a model that allowed researchers to create a measure of not only how impulsive each participant's behaviour was, but to identify brain regions that play a role in assessing the relative value of such choices.
Researchers found that people who scored high for psychopathy showed greater activity in a region called the ventral striatum - known to be involved in evaluating the subjective reward - for the more immediate choice.
"We mapped the connections between the ventral striatum and other regions known to be involved in decision-making, specifically regions of the prefrontal cortex known to regulate striatal response," Buckholtz said.
"We found that connections between the striatum and the ventral medial prefrontal cortex were much weaker in people with psychopathy," he said.
The lack of connection is important, Buckholtz said, because this portion of the prefrontal cortex role is thought to be important for 'mental time-travel' - envisioning the future consequences of actions.
There is increasing evidence that prefrontal cortex uses the outcome of this process to change how strongly the striatum responds to rewards.
With that influence weakened, the value of the more immediate choice may become dramatically over-represented.
"The way we think of it is 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," Buckholtz said.
The effect was so pronounced that researchers were able to use the degree of connection between the striatum and the prefrontal cortex to accurately predict how many times inmates had been convicted of crimes.
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