Thalamo-cortical white matter connectivity-defined thalamic subarea volumes predict individual delay discounting

Delay discounting (DD), the tendency to favor smaller, immediate rewards over larger, delayed rewards, is associated with impulsivity and various psychiatric disorders. In this study, we investigated the role of the thalamus, a brain structure with multiple subdivisions that relays information to cortical regions, in influencing DD. We hypothesized that thalamic subdivisions play distinct roles in modulating individual impulsivity. After quality control, we included diffusion tensor imaging and DD behavioral task data from 149 participants, who were asked to choose between immediate and delayed rewards. Using a probabilistic tractography approach, the thalamus was segmented into connectivity-defined regions (CDRs) based on cortical connections. This allowed us to examine how the relative volumes of these specific subthalamic regions connected to the cortical areas influence DD. Our findings showed that larger thalamic CDRs linked to the medial prefrontal cortex (MPFC) were correlated with higher DD, indicating greater impulsivity. Supplementary analyses using exponential and extended hyperbolic models for calculating DD confirmed the association with the MPFC-connected thalamic region, demonstrating the robustness of the finding across different models. The study concludes that the thalamus, particularly its connections with the MPFC, plays a crucial role in modulating impulsivity and temporal decision-making. This illustrates how the interactions between the thalamus and different cortical regions affect impulsive decision-making and has implications for understanding human behaviors characterized by impulsivity.