Neural dynamics hierarchy in motor cortex and striatum across naturalistic behaviors

Mammals perform a wide range of movements actuated by diverse patterns of muscle activity. Primary motor cortex (M1) and striatum are implicated in controlling these movements, but how their activity dynamics are organized to accommodate such diversity is poorly understood. We developed a paradigm that enabled us to investigate neural dynamics across diverse motor behaviors in mice. In contrast to existing views, we found neither behavior-specific nor behavior- invariant organization in single-neuron activity, population-level covariation, and muscle activity correlation. Instead, the similarity of activity dynamics between behaviors varied differentially across behavior pairs, forming a hierarchical organization. The same hierarchical organization was shared between M1 and striatum, despite stronger muscle activity correlation in M1 and greater behavior specificity in striatum. Network modeling indicated that striatal activity is sufficient to drive hierarchical dynamics in muscle pattern-generating circuits. These hierarchical dynamics may reflect a tradeoff between behavioral specialization and generalization in motor system function.