What Is the Brainstem Control of Locomotion?

Locomotion in humans is defined as bipedal progression through stages of a gait cycle to move from one place to another while maintaining balance and posture. Locomotion can be categorized in temporal phases (initiation, actual locomotive episode/execution, and termination) or in behavioral categories (slow exploratory and fast speed locomotion). The motivation behind a locomotive episode may be driven by internal needs (goal driven from the motor cortex or emotion driven from the limbic system) or external environmental cues. Locomotion is mediated by a spinal central pattern generator (CPG) under the influence of the brainstem reticular formation and is integrated with control of muscle tone and posture. Control of gait, muscle tone, and posture involves complex interactions among the sensorimotor cortex, basal ganglia, basal forebrain, cerebellum, brainstem, and spinal cord.1-3 Pioneering studies in cats4 and monkeys5,6 and more recently in rodents7-12 have contributed to elucidate the brainstem mechanisms controlling locomotion. This information, together with indirect evidence from human electrophysiologic and functional neuroimaging studies, provides testable pathophysiologic hypotheses and potential therapeutic targets for gait control disorders. The focus of this review is on brainstem mechanisms controlling locomotion. The role of other CNS areas in control of gait and posture and their abnormalities in disorders such as Parkinson disease (PD) have been extensively reviewed1 and are only briefly discussed here.