Can the period of postnatal codevelopment of the rubrospinal and corticospinal systems provide new insights into refinement of limb movement?

The corticospinal and the rubrospinal tracts are thought to synergistically contribute to the limb control during motor development. Williams et al. (J Neurosci 34: 4432-4441, 2014) demonstrate that the postnatal maturation of red nucleus motor map and the rubrospinal tract develops earlier than the corticospinal tract, to support early forelimb control. They have two distinct phases of maturation; a "precorticospinal" phase characterized by development of the rubrospinal system, and a "cocorticospinal" phase where they overlap with corticospinal development.