A meta-analysis of neural systems underlying delay discounting: implications for transdiagnostic research

The National Institute of Mental Health launched the Research Domain Criteria (RDoC) initiative to identify common biological mechanisms underlying mental disorders. A central challenge for this approach is to identify reliable biobehavioral paradigms that engage specific neural circuits implicated across psychiatric disorders. Delay discounting paradigms have been proposed as a promising candidate because both excessive and insufficient tendency to discount future rewards have been reported across a wide range of diagnoses. Because delay discounting involves multiple facets of neurocognitive functions, identifying specific neural systems engaged during the task can inform ongoing efforts in clinical neuroscience to link neural patterns to a core symptom dimension. To this end, we conducted a meta-analysis of 72 fMRI studies of delay discounting by common analytic approaches (contrasts) to test the predictions of commonly proposed mechanisms underlying the decision-making process. Despite being widely used in previous studies, comparing impulsive and patient choices did not reveal any reliable clustering of effects. Our results instead revealed that the subjective value, magnitude, and delay contrasts reliably engage the valuation network, with the subjective value contrast eliciting more widespread activation. Furthermore, both the difficulty and task contrasts engage the frontoparietal network. Taken together, our findings suggest that both reward valuation and action selection are important but do not fully explain impulsive versus patient choices. Taken together, these results provide further support that delay discounting task is a promising measure of reward valuation that reliably activates the valuation network. In addition, we discuss implications for analytic strategies for future studies in clinical neuroscience. ### Competing Interest Statement The authors have declared no competing interest.