Individuals who are willing to work hard even in the face of long odds have a stronger response to dopamine in regions of the brain associated with the reward centers of the brain, according to a new study published the Journal of Neuroscience. Conversely, individuals who are less willing to expend such effort have a greater response to dopamine in an area of the brain linked with social behavior and perception.
Previous work in animals had suggested that the dopamine system in the brain is an important mediator of cost benefit decision-making. These studies had probed the effects of manipulating the dopamine system on animals willingness to pursue food rewards. These studies had either enhanced or blocked the dopamine receptors in the animals. A few human studies had suggested that such manipulations of the dopamine system may also dampen or enhance an individuals willingness to pursue a reward. However, a team of researchers from Vanderbilt University wondered how much individual differences effected human decision-making. So the team recruited 25 healthy volunteers and subjected them both to behavioral testing of their willingness to complete tasks for potential monetary reward and positron emission tomography to measure individual brain responses to dopamine.
The scientists found that individuals who were more willing to complete tasks in the hopes of even a small chance at reward had greater dopaminergic activity in the striatum and prefrontal cortex—brain regions known to mediate motivation. Surprisingly, the researchers also found that individuals who were less likely to attempt such tasks had greater activation of the dopamine system in the insula, suggesting that this area may play a greater role in processing cost information. The authors conclude that a tendency to work hard is likely a trait determined by differences in region response to dopamine in the brain.
In addition to providing an explanation for certain human tendencies, the findings may have clinical implications for drugs that target the dopamine system such as antidepressants, and for conditions such as drug dependence that have been associated with dysfunction in the dopamine system.
“These results show for the first time that increased dopamine in the insula is associated with decreased motivation — suggesting that the behavioral effects of dopaminergic drugs may vary depending on where they act in the brain,” said lead author Michael T. Treadway, a graduate student at Vanderbilt.