An Integrative Theory of the Noradrenaline System: Meta-Control through Expected Information Gain

Living organisms constantly balance exploration and exploitation to adapt to changing environments.While the neuromodulator noradrenaline (NA) is known to regulate arousal, attention, and informationseeking, its precise computational function remains elusive. Here, we propose an integrative theory ofthe noradrenergic system, suggesting that it encodes expected information gain (EIG), a measure of howinformative the environment is over time, and that it uses this quantity for the meta-control of adaptivebehavior. We illustrate this theory using a hierarchical active inference model in which the NA systemacts as a higher-level meta-controller that dynamically adjusts a set of parameters (η) of a lower-levelbehavioral controller, modulating exploration rate, the balance between deliberative and habitual control,perceptual precision, learning rate, and cognitive flexibility. Simulations demonstrate that NA-basedEIG estimation and meta-control enhance performance in volatile environments by promoting directedexploration, facilitating rapid shifts away from maladaptive habits, sharpening sensory evidence, andaccelerating learning following context changes. These results unify multiple facets of noradrenergicfunction under a single computational objective, providing a novel perspective to explain tonic andphasic NA activity in estimating EIG and meta-controlling behavior. Summing up, this frameworkprovides a principled link between neuromodulation, exploration, and adaptive behavior, suggestingthat the noradrenergic system implements a fundamental mechanism for inferring and exploiting theinformational richness of the environment.