Mechanisms of premotor-motor cortex interactions during movement initiation

Preparing and initiating movements at the right time is critical for goal-directed behavior. Before movement execution, motor cortical areas exhibit preparatory activity, which decreases from premotor to primary motor areas. During the shift from preparation to execution activity in neural state space transitions from movement-null to movement-potent dimensions. However, the circuit-level mechanisms underlying this shift remain unresolved. Here, we demonstrate that projections from the rat premotor cortex (rostral forelimb area [RFA]) to the primary motor cortex (caudal forelimb area [CFA]) encode primarily pre-movement activity. Optogenetic inhibition of these projections has behavioral effects comparable to inhibiting either RFA or CFA alone. During preparation, RFA projections enhance and suppress CFA neurons similarly, affecting activity along CFA's preparatory dimension. During movement, RFA's influence shifts predominantly to excitatory, aligning with CFA's movement-potent dimension. These results establish a mechanistic link between neural state space concepts and underlying circuit mechanisms, providing an intuitive model for movement control.