Neural substrates underlying the expectation of rewards resulting from effortful exertion

Abstract

Decisions to exert effort for reward are often conceptualized as reflecting a trade-off between anticipated benefits and effort costs. However, economic theories propose that valuation is reference-dependent, such that behavior is shaped relative to expected outcomes rather than absolute reward magnitude. Whether reward expectations influence effort expenditure through such reference-dependent mechanisms, and how these computations are represented in the brain, remains unclear. Using an incentivized grip-force task during functional magnetic resonance imaging, we experimentally manipulated reward expectations independently of reward outcomes. Behavioral results showed that effort exertion varied systematically with reward expectations, indicating that individuals evaluated exertion relative to a reference point. Neural activity in the ventral striatum tracked both prospective reward expectations and deviations between expected and realized earnings. Moreover, these neural signals predicted individual differences in reference-dependent modulation of effort. Together, these findings identify ventral striatal representations associated with reference-dependent effort valuation and suggest that reference-dependent computations contribute to motivated behavior. Significance statementDecisions to exert effort are commonly described as reflecting a trade-off between reward and effort cost. However, whether effort valuation is shaped by reward expectations rather than absolute incentives remains unclear. Using functional magnetic resonance imaging and an incentivized grip-force task, we show that reward expectations serve as a reference point that systematically influences effort expenditure. Neural signals in the ventral striatum tracked both reward expectations and deviations between expected and realized outcomes, and these signals predicted individual differences in reference-dependent effort behavior. These findings suggest that reference-dependent valuation contributes to the neural control of motivated action.