Shared striatal neurons exhibit context-specific dynamics for internally and externally driven actions

Animals can initiate movements either in response to external cues or from internal drive, yet how the brain flexibly supports both remains unclear. Disorders such as Parkinson's disease disrupt these modes differently, suggesting distinct underlying mechanisms. These differences could arise from specialized circuits or from shared neuronal populations that shift their dynamics across contexts. To distinguish between these possibilities, we performed two-photon calcium imaging in the dorsolateral striatum as mice executed the same lever press either spontaneously or in response to a cue. Unsupervised clustering identified neurons modulated during cue, movement, or postaction periods. Critically, the same neurons encoded movement across initiation contexts, but their population dynamics diverged before movement. Both D1- and D2-expressing spiny projection neurons contributed to these dynamics, with D1-SPNs more active at the time of the sensory stimulus. These results show that context shapes neural dynamics within a shared movement-encoding population, revealing a context-generalizable striatal code that supports flexible movement initiation across internal and external drives.