Neural substrates underlying the expectation of rewards resulting from effortful exertion
Expectations as a reference point shape our decisions to motivate effortful activity. Despite the important role of reference points in human performance, little is known about how the brain processes expectations to guide motivated exertion. Participants completed a reward-based effort task in an MRI scanner. During each trial, participants were presented with a risky option that would either result in a fixed monetary payment, regardless of their effort exertion, or a piece-rate payment where the payment was proportional to the amount of effort exerted. We found that participants exerted more effort as the fixed payment increased, suggesting that the fixed payment influenced the reference point for effort exertion. The strength of this reference-dependent behavior was correlated with neural activity in the ventral striatum, which was significantly modulated by the deviation from the payoff to reward expectations after effort exertion. Our results suggest that value-related brain areas, particularly the ventral striatum, encode expectations of reward as a reference point to motivate effort exertion.