The predictive processing embodied in brain conditions: the role of precision.

Predictive coding theory proposes that the brain continuously minimizes prediction errors through hierarchical inference. Increasing evidence, however, suggests that its explanatory power depends not only on prediction generation, but also on precision weighting, the process through which the brain estimates the reliability of sensory, interoceptive, and contextual signals. Within this framework, psychological and psychiatric phenomena may arise from maladaptive precision allocation, leading to altered salience attribution, distorted inference, and inflexible behavioural responses. Neuromodulatory systems are increasingly recognized as critical biological substrates of these processes, regulating the gain assigned to prediction errors across cortical hierarchies. Neurotransmitters such as acetylcholine, dopamine, noradrenaline, and serotonin appear to differentially modulate attention, uncertainty estimation, salience, and contextual updating, thereby shaping perception, learning, and action. From this perspective, psychopathology may be conceptualized as a disorder of embodied precision regulation emerging from disruptions in neuromodulatory control over perceptual, affective, and contextual inference.