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Blunted Reward Prediction Error Encoding Drives Diminished Motivation to Explore in Apathy Associated With Traumatic Brain Injury

Hogeveen, J.; Campbell, E. M.; Aragon, D. F.; Pearson, E.; Enders, C.; Romero, J. D.; Brown, L.; Campbell, R. A.; Gill, D.; Quinn, D. K.; Husain, M.; Mayer, A. R.; Costa, V. D.

2025-08-26 neurology
10.1101/2025.08.22.25334260 medRxiv
Show abstract

Humans often prefer familiar, safe rewards to avoid the cognitive effort required to explore novel options. Here, we examined patients with motivational deficits following traumatic brain injury (TBI) as a clinical model to understand the neural mechanisms driving this trade-off. Participants with TBI and healthy controls performed two well-powered, model-based fMRI tasks: i) a physical effort-value tradeoff task, and ii) an explore-exploit decision-making task. While diminished motivation (i.e., apathy) in both groups was associated with a devaluation of prospective reward based on physical effort, TBI patients showed a distinct deficit in the motivation to explore novel opportunities. Specifically, while TBI patients with acquired apathy sometimes selected novel options, they failed to adequately weight the latent future value of the information that these options provided. This indicates that their exploration was more random rather than directed. This inability to track the "exploration bonus" of novel options in acquired apathy was also linked to impaired reward prediction error (RPE) encoding in key decision-making circuitry, including prefrontal cortex and the striatum. These findings suggest that RPE serves as a critical teaching signal, transforming random sampling into directed exploration.

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