Topographical distribution of structural impairments mediating increased impatience for reward

Abstract Choices involving trade-offs between larger later (LL) and smaller sooner (SS) rewards—a process known as delay discounting—are altered in many psychiatric and neurodegenerative conditions, leading to a preference for immediate rewards. The neural bases of this alteration remain unclear. Behavioral variant frontotemporal dementia (bvFTD), a neurodegenerative disorder marked by prefrontal atrophy, provides a neuropathological model to investigate structural impairments linked to increased discounting (higher reward impatience). We studied 22 bvFTD patients and 17 matched controls, using two delay discounting tasks involving monetary and food rewards to assess effects across secondary and primary rewards. We compared discount rates between groups and examined correlations with bvFTD symptoms. We then applied whole-brain mediation analysis to participants’ structural MRI data to identify neural mediators of increased discounting in bvFTD. Results showed higher discount rates in bvFTD for both money and food, which correlated with symptoms reflecting heightened impatience. Whole-brain mediation identified reduced grey matter density in the medial pulvinar, parahippocampal cortex, and middle temporal lobe as mediating this behavioural alteration. As discounting is disrupted in various psychiatric and neurological disorders, these structures may represent transdiagnostic neural markers of impatience for reward. Future research should assess whether these findings generalize across conditions.