Probing the neural substrates of movement generation across the rodent behavioral repertoire*

Mammals are generalists, capable of flexibly deploying movements across a range of behavioral contexts. However, existing paradigms for studying the genesis of movement in the brain often probe only a narrow range of highly trained behaviors, leaving the neural mechanisms that support this flexibility unclear. To extend the range of behaviors and contexts that can be studied, we developed a new behavioral monitoring system, CAPTURE, that combines motion capture and deep learning to track the 3D movements of twenty points on a freely behaving rat's trunk and appendages, continuously over week-long timescales. We combined CAPTURE with continuous neural recordings in the dorsolateral striatum, a brain region with a known, if debated, role in controlling diverse aspects of movement and behavior. Within individual behavioral states, striatal neurons displayed tuning to kinematic and behavioral variables. However across states, these tuning properties changed, in a manner that improved the within-state behavioral decodability. This suggests that context-specific coding may be a means to efficiently represent behavioral variables that are flexibly deployed across states, and that representational findings observed in tasks may fail to generalize.