Contributions of Intrinsic and Extrinsic Reward Sensitivity to Apathy: Evidence From Traumatic Brain Injury

Objective: Apathy is a key feature of traumatic brain injury (TBI). However, mechanisms underlying apathy are poorly understood. Evidence suggests that changes in reward may be a crucial factor. Rewards can come from two important sources: extrinsic reward (e.g., money) and intrinsic reward (e.g., enjoyment). Here, we used an experimental paradigm to examine the contributions of intrinsic-extrinsic reward sensitivity to apathy post-TBI and neurocognitive processes associated with these reward processing components. Method: Fifty-seven patients with TBI (TBI with clinical/severe apathy [TBI+sA], TBI with subclinical/moderate apathy [TBI+mA] and TBI without apathy [TBI-A] groups), and 30 healthy individuals completed the "birthday-gift task." In the "intrinsic reward" condition, participants chose to "go" to collect the gift or "wait" for the same gift to be delivered. In the "extrinsic reward" condition, the task was identical, however, participants received monetary incentives when choosing "going" instead of "waiting." The Montreal Cognitive Assessment was utilized for cognitive examination. Results: A smaller proportion of people in the TBI+sA group had high sensitivity to both intrinsic and extrinsic rewards than the TBI+mA, TBI-A and healthy comparison groups. The TBI+sA group also perceived the "go" option on the intrinsic reward condition as more effortful and made fewer "go" decisions on the extrinsic condition. Attention was the only predictor of intrinsic reward sensitivity, whereas executive functioning, attention and group predicted extrinsic reward. Conclusion: This study demonstrates the relationship between intrinsic-extrinsic reward hyposensitivity and apathy post-TBI. These results may be integrated into future trials to improve apathy in clinical practice. Key Points Question: Is apathy, a common and disabling behavioral problem after traumatic brain injury, associated with changes in intrinsic and extrinsic reward processing? Findings: The reduction of both intrinsic and extrinsic reward sensitivity has a crucial contribution to apathy following traumatic brain injury. Cognitive mechanisms associated with these difficulties appeared to be at least partly dissociable. Importance: This experimental study underscores the importance of considering both intrinsic and extrinsic components of reward processing deficits in providing comprehensive assessment of apathy and so effective interventions after TBI. Next Steps: Future research could take