Dopaminergic modulation of human inter-temporal choice: a diffusion model analysis using the D2-receptor-antagonist haloperidol.
The neurotransmitter dopamine is implicated in diverse functions, including reward processing, reinforcement learning and cognitive control. The tendency to discount future rewards in value over time has long been discussed in the context of potential dopaminergic modulation. Here we examined the effect of a single dose of the D2 receptor antagonist Haloperidol (2mg) on temporal discounting. Our approach extends previous human pharmacological studies in two ways. First, we applied state-of-the-art computational modeling based on the drift diffusion model to comprehensively examine choice dynamics. Second, we examined dopaminergic modulation of reward magnitude effects on temporal discounting. Drift diffusion modeling revealed reduced temporal discounting and substantially faster non-decision times under Haloperidol. Temporal discounting was substantially increased for low vs. high reward magnitudes, but this magnitude effect was largely unaffected by Haloperidol. These results were corroborated by model-free analyses as well as modeling via more standard approaches using softmax action selection. We previously reported elevated caudate activation under Haloperidol in this sample of participants, supporting the idea that Haloperidol elevated dopamine neurotransmission, e.g. by blocking inhibitory feedback via presynaptic D2 autoreceptors. The present modeling results show that during inter-temporal choice, this leads to attenuated temporal discounting and increased response vigor (shorter non-decision times).