Apathy as a failure of active inference

Apathy is a common symptom across a wide range of neurodegenerative and psychiatric conditions, characterised by a loss of goal-directed action. It is associated with faster rates of cognitive and functional decline, poor prognosis, and high caregiver burden. Effective treatments remain elusive. In this article, we propose that apathy is not merely the result of actions becoming undesirable due to insufficient reward or an inflated sense of cost. Instead, actions become unnecessary due to a loss of prior precision on action outcomes in the context of the 'Bayesian brain'. We outline the theoretical background and current evidence to support this framework and propose testable hypotheses regarding the behaviour, neuroanatomy, and neuropharmacology of apathy.