Corticospinal tract interaction in locomotor development and motor units formation: an hypothesis

In rat and kitten postnatal development the Corticospinal Tract (CST) growth has a temporal relationship with the development of mature locomotion and the elimination of polyneuronal innervation, and the formation of motorunits in the hindlimb muscles. This temporal correlation suggests a possible interaction of the CST with spinal motoneurons in the formation of functional groups of motorunits. Further, evidence is also given that spinal motoneuron size is plastic in the polyneuronal period; this indicates that motoneurons adapt themselves to their motorunits in postnatal life. This hypothesis suggests a causal interaction among these three neuronal events; the relevance of this interaction to the maturation of locomotor function is discussed.