Circuit Modules for Flexible Locomotion.

Locomotion, like all behaviors, possesses an inherent flexibility that allows for the scaling of movement kinematic features, such as speed and vigor, in response to an ever-changing external world and internal drives. This flexibility is embedded in the organization of the spinal locomotor circuits, which encode and decode commands from the brainstem and proprioceptive feedback. This review highlights our current understanding of the modular organization of these locomotor circuits and how this modularity endows them with intrinsic mechanisms to adjust speed and vigor, thereby contributing to the flexibility of locomotor movements.