Striatal Pathways for Action Counting and Steering.

The basal ganglia (BG) are critical for coordinating voluntary movements, yet their precise contribution remains a subject of debate. Using a novel operant counting task, we trained mice to perform a specific number of lever presses to obtain a reward, enabling quantification of continuous kinematics, discrete actions, and action sequences. Optogenetic manipulations of direct pathway (dSPN) and indirect pathway (iSPN) striatal projection neurons exert bidirectional and dissociable influences on both movement steering and action count progression: activation of dSPNs extends press sequences as if resetting an internal accumulator, whereas activation of iSPNs prematurely terminates them, mimicking completion of the count. In vivo calcium imaging reveals distinct yet intermixed populations of dSPNs and iSPNs representing either lever approach or count progression, with ramping activity patterns consistent with accumulation and discharge dynamics. Importantly, the difference between dSPN and iSPN population activity scales with proximity to both spatial and count-based goals, unifying discrete and continuous control within a push-pull model. These findings establish the BG as a central circuit for integrating kinematic and sequential representations to monitor and steer progress toward behavioral goals.