Astrocytes in the External Globus Pallidus Selectively Represent Routine Formation During Repeated Reward-Seeking in Mice

The external globus pallidus (GPe) is a central part of the basal ganglia indirect pathway implicated in movement and decision-making. As a hub connecting the dorsal striatum and subthalamic nucleus (STN), the GPe guides repetitive and routine behaviors. However, it remains unknown how diverse GPe cells engage in routine formation while learning action sequences in repetitive reward-seeking conditioning. Here, in male mice, we investigated the Ca dynamics of two GPe cell types, astrocytes and parvalbumin-expressing neurons, during routine formation. Our findings show that the dynamics of GPe astrocytes may be involved in action sequence refinement, a characteristic potentially contributing to more efficient reward-seeking behavior. The ability to form and refine action sequences is essential for both survival and efficiency. In this study, we introduced the "routine index", a measure that captures how consistently animals repeat a specific action sequence to maximize rewards. This tool provides a systematic approach to measure and analyze subject's transition from varied to consistent and optimized behaviors. Furthermore, we demonstrate that Ca dynamics of astrocytes, not neurons, within the external globus pallidus (GPe) correlate with this index, highlighting their active role in representing routine behaviors. These insights not only deepen our understanding of astrocytic functions in neural circuits, but also pave the way for potential therapeutic interventions for disorders characterized by impaired decision-making and habitual behaviors.