The fatigue conundrum

Abstract

Fatigue is a major affective symptom in neurological disease, but its basis is poorly understood. Kuppuswamy describes the defining features of fatigue and its relationship to perceived effort, before proposing that pathological fatigue is a consequence of impaired sensory attenuation.

Figure 1

A schematic representation of how sensory attenuation may underpin perceived effort during movement, using the active inference framework of sensorimotor control. The descending commands from the brain specify sensory predictions (Efferents) that are compared with the incoming sensory signals (Afferents)—giving rise to sensory prediction errors (Prediction-Sensory Input = Prediction Error). ‘To attend or not to attend’ to the sensory prediction errors, which drive motor output (Descending Prediction Error), depends on the precision the brain affords them (Ascending Prediction Error). When sensory precision is high, prediction errors are heeded to, which I hypothesize gives rise to high perceived effort. On the contrary, when sensory precision is attenuated, afferent sensory errors are ignored resulting in sense of effortlessness. In conditions where sensory attenuation is impaired, incongruent perceived effort may arise leading to perceptual feeling of fatigue.