Parkinson’s medication has opposite effects on two kinds of motivation

Patients with Parkinson’s disease lack the brain chemical dopamine. Dopamine is thought to signal upcoming rewards, and this might explain why patients on treatment can develop impulse control disorders.

My lab is studying two different ways to motivate people. One way is to reward or punish them based on how well they do — like performance-related pay. The other way is to promise a guaranteed reward, which also tends to keep people motivated (even though they don’t have to). Both these kinds of motivation have been linked to dopamine in different ways.

In our study (Grogan et al. 2021), we found that dopamine boosted performance-related motivation. This may be because it helps patients act ‘instrumentally’, amplifying the contingency between their actions and the rewards. And surprisingly, dopamine also reduced the effect of guaranteed rewards.

The results suggest that giving dopamine in Parkinson’s doesn’t directly increase reward sensitivity, but rather, increases the coupling between incentives and actions.