An fMRI-Based Brain Marker of Individual Differences in Delay Discounting

Individual differences in delay discounting-how much we discount future compared to immediate rewards-are associated with general life outcomes, psychopathology, and obesity. Here, we use machine learning on fMRI activity during an inter -temporal choice task to develop a functional brain marker of these individual differences in human adults. Training and cross-validating the marker in one dataset (Study 1, N = 110 male adults) resulted in a significant prediction-outcome corre-lation (r = 0.49), generalized to predict individual differences in a completely independent dataset (Study 2: N = 145 male and female adults, r = 0.45), and predicted discounting several weeks later. Out-of-sample responses of the functional brain marker, but not discounting behavior itself, differed significantly between overweight and lean individuals in both studies, and predicted fasting-state blood levels of insulin, c-peptide, and leptin in Study 1. Significant predictive weights of the marker were found in cingulate, insula, and frontoparietal areas, among others, suggesting an interplay among regions asso-ciated with valuation, conflict processing, and cognitive control. This new functional brain marker is a step toward a gener-alizable brain model of individual differences in delay discounting. Future studies can evaluate it as a potential transdiagnostic marker of altered decision-making in different clinical and developmental populations.

Automated summary

Individual differences in delay discounting, associated with various life outcomes, psychopathology, and obesity, were studied using machine learning on fMRI activity during inter-temporal choice tasks. A functional brain marker was developed and validated in two independent datasets, with significant correlations to prediction outcomes and long-term discounting behavior. The marker also showed differences between overweight and lean individuals and predicted blood levels of insulin, c-peptide, and leptin.