Dopamine boosts motivation for prosocial effort in Parkinson's disease.

Being willing to exert effort to obtain rewards is a key component of motivation. Previous research has shown that boosting dopamine can increase the willingness to choose to exert effort to obtain rewards for ourselves. Yet often we must choose whether to exert effort, not for our own immediate benefit, but to be prosocial and obtain a benefit for someone else. Pharmacologically increasing dopamine availability has been shown to change social behaviours in experimental tasks, and dopamine degeneration in Parkinson's Disease (PD) impacts a range of socio-cognitive processes. However, the neuromodulators involved in deciding whether to exert effort to benefit others are unknown. Does dopamine modulate the willingness to exert prosocial effort? Here, male and female PD patients (n=37) ON or OFF their dopaminergic medication completed a task where they chose whether to put in effort for larger reward, or rest and receive a smaller reward, on separate trials either to benefit themselves ('self') or an anonymous other person ('other'). PD patients were more willing to exert effort to benefit themselves than another person, a pattern also observed in an age- and gender-matched control group (n=42). However, crucially PD patients had increased willingness to exert effort for other relative to self, ON compared to OFF medication. These results suggest that dopamine augmentation in PD can increase levels of prosocial motivation, highlighting a key role for dopamine in motivation beyond obtaining rewards for ourselves. Prosocial behaviours - acts that benefit other people - are fundamental for societal cohesion. Often prosocial acts, such as helping a friend move home, are effortful. However, the neurochemicals involved in choosing to put effort into prosocial acts are unknown. Dopamine is involved in motivating people to exert effort to obtain themselves rewards, but does it also make us choose to put more effort into prosocial behaviours? We find that dopamine depleted Parkinson's Disease patients are more willing to choose to put effort into prosocial acts ON dopamine boosting medication compared to OFF. These results provide the first insight into the neurochemicals underlying prosocial effort, and highlight dopamine as key to working hard to help others.