Prefrontal Brain Microstructural Integrity is Related to an Exploitation Bias in Older Adulthood

Abstract

The exploration–exploitation trade-off reflects a fundamental decision-making process supported by interactions between cortical regions involved in reward valuation and monitoring and subcortical systems that regulate attention and learning. In previous work, we demonstrated that microstructural integrity of the locus coeruleus (LC), assessed with quantitative MRI (qMRI), predicts individual differences in explore-exploit behavior in older adults. Building on these findings, we examined whether similar structure–function relationships exist within cortical regions implicated in explore-exploit. In typically aging older adults (N=109), we collected magnetization transfer saturation (MTsat), a qMRI measure sensitive to cellular microstructure, to assess integrity of the medial orbitofrontal cortex (mOFC), frontopolar cortex (FPC), rostral middle frontal gyrus (rMFG), and dorsal anterior cingulate cortex (dACC). Lower MTsat in the mOFC, FPC, and rMFG and decreasing MTsat across time was associated with an exploitation bias. Dominance analysis revealed FPC MTsat as the strongest predictor of exploitative decision-making in older adulthood.