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, 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.