The evolution of the primitive stepping response in newborns

Stepping responses can be evoked in neonates but are irregular and characteristically disappear 4–6 weeks after birth and reappear at age 6–8 months. There are different hypotheses about the development of motor patterns. Italian researchers compared basic patterns of lumbosacral motor neurone activity from multi-muscle recordings in stepping neonates, toddlers, pre-school children and adults.[1] They recorded kinematics, contact forces and electromyographic activity from up to 24 muscles simultaneously. Surprisingly, they found that the two basic patterns of stepping neonates were retained throughout development and augmented by two new patterns, which first appeared in toddlers. Very similar patterns were observed also in the rat, cat, macaque and guineafowl, which suggest that despite substantial phylogenetic distances and morphological differences, locomotion in several animal species starts from common primitive origins, perhaps related to a common ancestral neural network.

Reviewer: David Isaacs,, Children's Hospital at Westmead, Sydney