Apathy is associated with reduced precision of prior beliefs about action outcomes
Apathy is a debilitating syndrome that is associated with reduced goal-directed behaviour. Although apathy is common and detrimental to prognosis in many neuropsychiatric diseases, its underlying mechanisms remain controversial. We propose a new model of apathy, in the context of Bayesian theories of brain function, whereby actions require predictions of their outcomes to be held with sufficient precision for explaining away differences in sensory inputs. In this active inference model, apathy would result from reduced precision of prior beliefs about action outcomes. Healthy adults (N=47) performed a visuomotor task that independently manipulated physical effort and reward, and served to estimate the precision of priors. Participants perception of their performance was biased towards the target, which was accounted for by precise prior beliefs about action outcomes. Crucially, prior precision was negatively associated with apathy. The results support a Bayesian account of apathy, that could inform future studies of clinical populations.