Connecting Circuits for Supraspinal Control of Locomotion.

Locomotion is regulated by distributed circuits and achieved by the concerted activation of body musculature. While the basic properties of executive circuits in the spinal cord are fairly well understood, the precise mechanisms by which the brain impacts locomotion are much less clear. This Review discusses recent work unraveling the cellular identity, connectivity, and function of supraspinal circuits. We focus on their involvement in the regulation of the different phases of locomotion and their interaction with spinal circuits. Dedicated neuronal populations in the brainstem carry locomotor instructions, including initiation, speed, and termination. To align locomotion with behavioral needs, brainstem output structures are recruited by midbrain and forebrain circuits that compute and infer volitional, innate, and context-dependent locomotor properties. We conclude that the emerging logic of supraspinal circuit organization helps to understand how locomotor programs from exploration to hunting and escape are regulated by the brain.