Spinal circuitry of sensorimotor control of locomotion

During locomotion many segmental hindlimb reflex pathways serve not only to regulate the excitability of local groups of motoneurones, but also to con trol the basic operation of the central pattern-generating circuitry respon sible for locomotion. This is accomplished through a reorganization of refl exes that includes the suppression of reflex pathways operating at rest and the recruitment during locomotion of previously unrecognized types of spin al interneurones. In addition presynaptic inhibition of transmission from s egmental afferents serves to regulate the gain of segmental reflexes and ma y contribute to the selection of particular reflex pathways during locomoti on. The fictive locomotion preparation in adult decerebrate cats has proved to be an important tool in understanding reflex pathway reorganization. Fu rther identification of the spinal interneurones involved in locomotor-depe ndent reflexes will contribute to our understanding not only of reflex path way organization but also of the organization of the mammalian central patt ern generator.