The researchers' brain imaging study reveals that the "go-getters" who work hard for rewards had higher release of the neurotransmitter dopamine in the striatum and ventromedial prefrontal cortex, the areas of the brain known to play an important role in reward and motivation. "Slackers," meanwhile, had high dopamine levels in the anterior insula, another brain area that plays a role in emotion and risk perception.
“Past studies in rats have shown that dopamine is crucial for reward motivation,” explained Vanderbilt post-doctoral student Michael Treadway, “but this study provides new information about how dopamine determines individual differences in the behavior of human reward-seekers.”
Researchers studied 25 healthy volunteers (52 percent female) ranging in age from 18 to 29. To determine their willingness to work for a monetary reward, the participants performed a button-pushing task. First, they were asked to select either an easy or difficult task. Easy tasks earned $1 while the reward for hard tasks ranged up to $4. Once they made their selection, they were told they had a high, medium or low probability of getting the reward. Individual tasks lasted for about 30 seconds and participants were asked to perform them repeatedly for about 20 minutes.
“At this point, we don’t have any data proving that this 20-minute snippet of behavior corresponds to an individual’s long-term achievement,” said David Zald, a Vanderbilt professor of psychology, “but if it does measure a trait variable such as an individual’s willingness to expend effort to obtain long-term goals, it will be extremely valuable.”
The fact that dopamine can have opposing effects in different parts of the brain complicates the picture regarding the use of psychotropic medications that affect dopamine levels for the treatment of attention-deficit disorder, depression and schizophrenia because it calls into question the general assumption that these dopaminergic drugs have the same effect throughout the brain.
The study was published May 2 in the Journal of Neuroscience. The research was funded by The National Institute of Drug Abuse.
