Dopamine Increases Our Sensitivity to Benefits
Post by D. Chloe Chung
What's the science?
We tend to avoid certain tasks that require too much work because our brain thinks that the costs of completing them will outweigh the benefits that we will receive. The neurotransmitter dopamine has been reported to mediate this process of comparing the costs and the benefits of cognitive work. Indeed, the brain-stimulating drug methylphenidate (or Ritalin) that is commonly used to treat attention-deficit/hyperactivity disorder (ADHD), increases the amount of dopamine in our synapses by preventing its reuptake. However, it’s still not well understood exactly whether dopamine increases willingness to expend cognitive effort or, if so, how. This week in Science, Westbrook, and colleagues show that dopamine increases our willingness to execute cognitively demanding tasks by increasing our sensitivity to their benefits.
How did they do it?
The authors recruited 50 healthy young adults and used positron emission tomography (PET) to measure the rate at which neurons synthesize dopamine in the brain, specifically in the striatum where dopamine is abundantly released. Next, the participants were asked to choose between a more difficult task that comes with a higher monetary reward and an easier task with a smaller reward. During this test, their eye movements were tracked to find out what components on the test screen they pay the most visual attention to the difficulty level of tasks (costs) or the amount of money they will receive upon task completion (benefits). This way, the authors were able to make connections between dopamine levels and what participants were most attentive to. The authors also wanted to understand how changing the dopamine level in the brain can impact people’s decisions to perform difficult tasks. To test this, participants received either dopamine-boosting drugs or a placebo while taking this test multiple times. Neither authors nor participants knew which drug was given at the time of these tests.
What did they find?
The authors first found that participants were more likely to avoid tasks the more cognitively challenging they were and in participants who synthesized dopamine more slowly. Interestingly, participants with a low dopamine level became more eager to perform difficult cognitive tasks when they received dopamine-enhancing drugs, showing that it’s possible to motivate people to do more cognitive work by manipulating dopamine levels. Based on a computer simulation, a higher dopamine level was predicted to make participants become more sensitive to the benefits and less sensitive to the costs of cognitive tasks. This prediction was proven to be correct, as participants with a high base level of dopamine and those whose dopamine level was increased with the drugs both showed higher sensitivity to the task benefits and lower sensitivity to the costs. Also, when participants paid more attention to benefits versus costs, they were more likely to choose to perform challenging tasks, suggesting that greater attention to benefits increases motivation. Importantly, this effect was amplified in individuals with higher dopamine levels, whether the high levels were present at baseline or only after drug administration, again highlighting the important role of dopamine in sensitizing our brain to benefits.
What’s the impact?
In this study, the authors show the first evidence that dopamine can motivate us to do difficult cognitive work by increasing the effects of benefits versus costs. Their findings suggest that dopamine-enhancing medications like Ritalin, which is often misused to improve focus while studying among students, exert their effects by increasing our willingness to invest cognitive efforts, rather than by making us “smarter”. Importantly, however, the effect seems to be restricted to people with low dopamine levels at baseline - those with high levels weren't helped and there was even some evidence that things got worse. This study will also help to inform future research on dopamine modulation in ADHD and other neurological disorders with impaired cognitive motivation, such as Parkinson’s disease.
Westbrook et al. Dopamine promotes cognitive effort by biasing the benefits versus costs of cognitive work (2020). Access the original scientific publication here.