Modular striatal dynamics and reciprocal inhibition orchestrate skilled action sequencing

The basal ganglia, particularly the striatum, are critical for orchestrating skilled behavioral sequences, yet the precise mechanisms underlying this process remain unclear. Using high-resolution kinematic tracking and neural recordings in mice performing a water-reaching task, we found spatially distributed modules of striatal projection neurons whose activity corresponded to the generation of each element in the sequence--aiming, reaching, and drinking. They are activated sequentially and exhibit reciprocal inhibition, ensuring a strict serial order. Optogenetic activation of the direct pathway of the orofacial module promoted licking while suppressing reaching. Reaching could in turn suppress stimulation-evoked licking, revealing bidirectional inhibitory interactions. Our findings demonstrate that the striatums modular organization, coupled with lateral inhibition, sculpts the temporal progression of actions, providing a mechanistic framework for understanding how the basal ganglia coordinate complex behaviors.