Organization of human locomotion: Proprioception and quadrupedal coordination

Most purposeful, complex movements are programmed in the central nervous system (CNS) and adapted by proprioceptive feedback. The selection of and interaction between different sources of afferent input is task dependent. For motor behaviors, such as locomotion, afferent input related to load and hip-joint position, probably, has an important role in the proprioceptive contribution to the activation pattern of the leg muscles. Recent research indicates that interlimb coordination during human locomotion is organized in a similar way to that in the cat. Hence, during locomotion, corticospinal excitation of upper limb motoneurons is mediated indirectly, via propriospinal neurons in the cervical spinal cord. This allows for a task-dependent neuronal linkage of cervical and thoraco-lumbar propriospinal circuits, controlling leg and arm movements during human locomotor activities