[Functional roles of spinal reflexes during human locomotor movements]

Understanding of the neural mechanisms underlying locomotion has been rapidly evolving on the basis of ample evidence obtained from chronic and acute experiments on quadrupedal animals. Rhythmic and alternative extensor and flex activity in quadrupedal locomotion is thought to be formed by central pattern generators (CPGs) that are deployed in each joint and located in the spinal cord. Descending inputs from the cerebral cortex, cerebellum, and mesencephalon would induce CPGs to generate and regulate locomotor rhythm and patterns. Afferent inputs would also play an important role in regulating CPGs. In humans, it is extremely difficult to provide direct evidence of CPGs because of experimental limitations. However, substantial evidence showing the existence of CPGs in humans has been provided by experiments investigating infant stepping, patients with spinal cord injuries, and electrical stimulation to the epidural cord. In addition, some reflexes were shown to be strongly controlled by CPGs during locomotor movements. Further investigation of the CPG system in humans would provide useful information for improving physical therapeutic methods and neurorehabilitation training for persons with gait disorder. The present article will review control mechanisms of spinal reflexes by CPGs in humans during locomotor movements.