Yury Ivanenko
Santa Lucia Foundation, Italy

Early development of human locomotion

How do we walk when we start to walk? This presentation will outline recent advances in understanding how motor commands are expressed at different stages of human development. The spinal locomotor output can be assessed by identifying the basic patterns of lumbosacral motoneuron (MN) activity from multimuscle recordings. The development of human locomotion from the neonate to the adult starts from a rostrocaudal excitability gradient in the spinal motor output and involves a gradual functional reorganization of the pattern generation circuitry and a progressive reduction of EMG burst durations with increasing age. It has been also argued that the nervous system may control numerous muscles through modularity, using neural patterns to activate muscles in groups called synergies. The alternating spinal motor output in neonates is consistent with a simpler organization of neuronal networks. The co-ordination of limb and body segments arises from the coupling of neural oscillators between each other and with limb mechanical oscillators. Despite millions of years of bipedal walking evolution, at the onset of walking, changes in vertical body loads are not compensated accurately by the kinematic controllers and the gravity-related pendulum mechanism of walking does not seem to be implemented, requiring each toddler to develop it. We discuss the precursor of the mature locomotor pattern in infants as an optimal starting point strategy for gait maturation.