The cognitive effects of a promised bonus do not depend on dopamine synthesis capacity

Abstract

Reward motivation is known to enhance cognitive control. However, detrimental effects have also been observed, which have been attributed to overdosing of already high baseline dopamine levels by further dopamine increases elicited by reward cues. Aarts et al. (2014) indeed demonstrated, in 14 individuals, that reward effects depended on striatal dopamine synthesis capacity, measured with [18F]FMT-PET: promised reward improved Stroop control in low-dopamine individuals, while impairing it in high-dopamine individuals. Here, we aimed to assess this same effect in 44 new participants, who had previously undergone an [18F]DOPA-PET scan to quantify dopamine synthesis capacity. This sample performed the exact same rewarded Stroop paradigm as in the prior study. However, we did not find any correlation between reward effects on cognitive control and striatal dopamine synthesis capacity. The discrepancy between the current and our previous findings might reflect the use of different radiotracers for indexing dopamine synthesis capacity. STATEMENT OF RELEVANCEReward motivation is generally thought to enhance cognitive control, but paradoxical negative effects of rewards on cognitive control have also been observed. A previous PET study demonstrated that reward effects on Stroop control depended on baseline striatal dopamine synthesis capacity, indexed by uptake of the radiotracer [18F]FMT. The sample size is this study was very small for a between-subject correlational design. Replicating the exact same Stroop paradigm within a larger sample is therefore crucial to robustly establish the mechanistic link between incentive motivation and cognitive control and advancing our understanding of who chokes under pressure and why, a topic of great societal relevance today. The present study did not reveal any correlation between reward effects on cognitive control and striatal dopamine synthesis capacity, indexed with [18F]FDOPA-PET. Future studies might consider putative differential sensitivity of the radiotracer [18F]FMT and [18F]FDOPA, while also addressing other indices of dopamine transmission.