Investigating associations of delay discounting with brain structure, working memory, and episodic memory

Garzón, Benjamín; Kurth-Nelson, Zeb; Bäckman, Lars; Nyberg, Lars; Guitart-Masip, Marc · 2023 · Crossref

DOI: 10.1093/cercor/bhac164

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Summary

This study investigates the neurobiological and cognitive correlates of delay discounting (DD), a behavioral measure reflecting the preference for immediate smaller rewards over larger delayed ones. While DD is relevant to psychopathology and daily functioning, previous research on its structural brain correlates has yielded inconsistent results, likely due to small sample sizes. The authors aimed to resolve these discrepancies by leveraging a large, openly available dataset to examine associations between DD, brain structure, and memory performance. The researchers analyzed data from 1,196 healthy younger adults from the Human Connectome Project (HCP). Participants completed a computerized intertemporal choice task to estimate their discount rates, as well as tests for working memory (WM) and episodic memory (EM). Structural magnetic resonance imaging data, including T1-weighted and diffusion-weighted imaging, were processed to assess cortical thickness, surface area, gray matter volume (GMV), subcortical volumes, and white matter microstructure (fractional anisotropy and mean diffusivity). The study employed linked independent component analysis (linked-ICA) to decompose structural data into covariance networks, alongside univariate voxel-wise and vertex-wise analyses. Statistical models controlled for age, sex, education, income, and general intelligence, while accounting for the familial structure of the HCP sample. The results indicated that greater delay discounting was significantly associated with smaller gray matter volume in the anterior temporal cortex. This finding was robust across different decomposition methods and remained significant after controlling for general intelligence. However, no significant associations were found between DD and total cortical volume, subcortical volumes, or markers of white matter microscopic organization. Furthermore, the study found no significant links between DD and performance on working memory or episodic memory tasks after adjusting for socioeconomic confounders. Previous reports linking DD to cortical volume or white matter integrity were not replicated, suggesting those findings may have been spurious or driven by insufficient statistical power. The authors conclude that the effects linking brain structure to delay discounting are small and require large sample sizes and rigorous statistical controls to detect reliably. The lack of association with white matter and memory tasks challenges existing theories regarding the cognitive mechanisms underlying DD. The study highlights the necessity of using large cohorts and methods that accommodate complex data structures to avoid false positives. It also underscores the need for improved task parameter reliability in future research to better understand the neural basis of intertemporal choice.

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• cognitive capacity variation