Impaired Adaptive Learning in Chronic Pain Contributes to Apathy

The cognitive mechanisms linking chronic pain to motivational symptoms remain poorly understood. We demonstrate that individuals with chronic temporomandibular disorder (TMD), a common cause of chronic pain, exhibit a specific deficit in adaptive learning in uncertain environments, characterized by failure to reduce uncertainty over time and maintain efficient learning rates. Using a probabilistic reward task, we pioneered the application of a novel volatile Kalman filter to model behavior in 26 TMD participants and 39 matched controls, uniquely tracking trial-wise updates in uncertainty, volatility, and learning rate. Although surface-level performance did not differ across groups, model-based analysis revealed that those with TMD failed to reduce uncertainty and adapt their learning over time. TMD participants also reported significantly greater apathy, depression, and pain catastrophizing, as well as lower health-related quality of life. Mediation analysis confirmed that impaired uncertainty adaptation partially mediated the relationship specifically between TMD and apathy. These findings identify a computational signature of disrupted uncertainty adaptation in people with TMD and provide evidence for a mechanistic link between chronic pain and motivational dysfunction. This work lays a foundation for future studies examining how belief-updating deficits contribute to broader affective and cognitive symptoms in chronic pain.