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

Area of Science:

• Neuroscience
• Cognitive Psychology
• Clinical Neurology

Background:

• Clinical apathy is characterized by reduced motivation, potentially arising from effort aversion or impaired exploration of future rewards.
• Chronic traumatic brain injury (TBI) is frequently associated with apathy, necessitating investigation into its underlying cognitive and neural mechanisms.

Purpose of the Study:

• To investigate the cognitive and neural bases of apathy in chronic TBI patients using fMRI during motivated choice tasks.
• To differentiate between effort-based decision-making deficits and impaired future-oriented exploration in TBI-related apathy.

Main Methods:

• Task-based functional magnetic resonance imaging (fMRI) was employed to assess motivated choice computations in TBI patients and healthy controls (CTRLs).
• Participants completed an effort-value tradeoff task ('Apples Task') and an explore-exploit tradeoff task ('Novelty-Bandit Task').
• Behavioral data and neural activity were analyzed in relation to apathy levels.

Main Results:

• Higher apathy correlated with increased effort-based discounting of rewards and heightened neural encoding of effort costs in both TBI and CTRL groups.
• In TBI patients, apathy was specifically linked to reduced valuation of information for future rewards, not impaired immediate value learning.
• This deficit in TBI was associated with blunted reward prediction error (RPE) encoding in prefrontal cortex and basal ganglia during feedback processing.

Conclusions:

• Apathy may involve a dual mechanism: a general aversion to effort and, uniquely in TBI, impaired future-oriented decision-making.
• Blunted RPE signaling in TBI patients degrades learning signals, hindering the exploration of novel opportunities and reducing future motivation.
• Targeting RPE-related neural networks offers a potential avenue for neuromodulatory interventions to improve motivation in TBI.