Orbitofrontal noradrenaline mediates volatility-dependent adjustment of learning rate
Adaptive decision-making in dynamic environments requires flexible adjustment of learning speed to balance stability and flexibility. When outcomes are highly stochastic, learners must avoid over interpreting noise and update more slowly, whereas in volatile environments where contingencies change frequently, learning should accelerate to rapidly incorporate new evidence. Theories propose that internal estimates of uncertainty tune learning rates through neuromodulatory-dependent mechanisms. Here, we investigated how noradrenergic inputs from the locus coeruleus (LC) to the orbitofrontal cortex (OFC) support adaptive learning under uncertainty. We show that rats performing a probabilistic reversal learning task exhibited behavior that was best explained by an adaptive reinforcement-learning model in which learning rates dynamically adjust according to estimated environmental volatility and stochasticity, outperforming standard fixed-rate models. Noradrenaline release in the OFC closely tracked trial-by-trial, model-derived volatility estimates around contingency changes. Disrupting LC[->]OFC noradrenergic inputs reproduced the model-predicted deficit in volatility-dependent adjustments of learning rate. Together, these findings identify OFC noradrenergic signaling as a key circuit mechanism for volatility-dependent modulation of learning rates during adaptive decision-making.