Circuit mechanisms of GPe pauses account for adaptive exploration

Abstract The external globus pallidus (GPe) has traditionally been viewed as a relay nucleus within the basal ganglia (BG), but accumulating evidence indicates a more dynamic role in reinforcement learning (RL). One key characteristic of GPe activity—transient pauses in high-frequency discharge (HFD) neurons—is preserved across species, yet its potential implications in RL remains unclear. Here, we developed a neurophysiologically grounded computational model to investigate the origin and role of GPe pauses in RL. Our model successfully replicated a range of empirical observations, including pause dynamics during learning and cue-related activity modulation. We demonstrated that the GPe-subthalamic nucleus (STN) circuit functions analogously to a denoising autoencoder, modulating baseline excitability in downstream BG circuits and that GPe pauses emerge as circuit-level consequences of strong, convergent inhibition from the GPe to STN. Simulations and in vivo recordings revealed that the activity of GPe-STN projecting neurons increases following sudden environmental changes, promoting adaptive exploration by disrupting action value contrast. Intriguingly, this same configuration impairs performance with extended training, suggesting that habitual behavior may benefit from weakened GPe-to-STN projections. These findings provide a unifying framework for understanding GPe pause dynamics and highlight circuit-level distinctions supporting the balance between flexibility and proficiency in RL.