Are you the kind of person who is always “on,” constantly driven to achieve? Or are you more of a slacker type, less motivated by the promise of material reward? The difference may lie in the responsiveness of the dopamine system in your brain, according to new research.Dopamine is believed to be the brain chemical that fuels will: it is critical for not only for psychological motivation, but also for physical movement. While people commonly associate dopamine with the zing of pleasure in the brain that accompanies everything from cocaine to kisses, the neurotransmitter’s effect in certain regions has more to do with reward — that is the anticipation of pleasure and the deliciousness of desire — than with pleasure itself (that feeling probably involves the brain’s opioids).
Previous studies have shown that lowering brain levels of dopamine reduces the willingness to work harder for greater rewards, both in animals and humans. So neuroscientists led by Michael Treadway, a graduate student at Vanderbilt University, sought to find out how varying levels of dopamine in people’s brains affected their motivation to work.
The researchers imaged the brains of 25 young adults as they played either an easy button-pressing game or a harder one, both for a monetary reward. The easy task, which involved pressing a button a certain number of times very quickly with the dominant index finger, could potentially pay out $1. The harder task, which required participants to use their non-dominant pinky finger, could earn them up to $4.30.
Before each round, participants were told their probability of winning, which was the same for the easy and hard tasks each time. Probability of winning was either low (12%), medium (50%) or high (88%).
Prior to the gaming, the participants had their brains imaged while under the influence of either amphetamine or placebo. This allowed researchers to measure the responsiveness of their dopamine systems, by gauging the availability of certain dopamine receptors. None of the participants was addicted to drugs or had attention deficit/hyperactivity disorder (ADHD) that required treatment with stimulants, and they were not under the influence of the drug when they later played the game.
The researchers found that participants who naturally chose to work harder — even when the chance of winning was low had higher levels of dopamine responsiveness in a brain region known as the striatum, an area classically linked with desire and pleasure. Those who put in greater effort also had more dopamine responsivity in the ventromedial prefrontal cortex, an area linked with drive and planning.
In contrast, people who tended to slack had higher responsiveness in the insula, an area that seems to focus on costs, rather than benefits — as in, “Gee, my pinky is tired” and also monitors internal body states like hunger, cold, pain and thirst.
The authors conclude that their research “provides novel evidence linking variation in human [dopamine] function with cost/benefit preferences.” They explain that problems with this kind of decision-making are seen in many psychiatric disorders, most notably depression — in which motivation can be entirely lost and addiction, which causes motivation to be wrongly directed.
However, it’s important to mention here what this study does not show: it doesn’t prove that these differences in dopamine responsiveness are genetic, nor does it show that they are immutable. It is a small trial and the results need to be replicated.
We already know that depression and addiction quite frequently remit, either naturally or with treatment, so changes in the system are clearly possible. And some people may slack on some types of tasks, but be highly motivated on others.
Importantly, previous research has also shown quite clearly that motivation can change. Indeed, taking drugs like amphetamine or Ritalin, for example, shifts people’s preferences towards high effort/high reward options and away from those requiring less effort and offering low reward. (This effect may vary according to people’s initial tendencies, however, if this rat research is anything to go by.)
So the potentially alarming implication here that some people may just be born to slack and would be terminally unable to compete with those who are inherently more driven is far from settled. Also unclear is whether people with low dopamine responsivity have other skills that could provide different advantages.
But if there do turn out to be innate differences in drive linked with dopamine (perhaps this is what we now label as ADHD?), it may be unfair not to allow those who wish to alter their motivation chemically to do so if the benefits outweigh the risks.