Motor cortex latent dynamics encode arm movement direction and urgency independently.

The fluid movement of an arm is controlled by multiple parameters that can be set independently. Recent studies argue that arm movements are generated by the collective dynamics of neurons in motor cortex. But how these collective dynamics simultaneously encode and control multiple parameters of movement is an open question. Using a task where monkeys made sequential, varied arm movements, we show that the direction and urgency of arm movements are simultaneously encoded in the low-dimensional trajectories of population activity: each movement's direction by a fixed, looped neural trajectory and its urgency by how quickly that trajectory was traversed. Network models showed this latent coding is potentially advantageous as it allows the direction and urgency of arm movement to be independently controlled. Our results suggest how low-dimensional neural dynamics can define multiple parameters of goal-directed movement simultaneously.