The role of independent walking in the maturation of the spinal locomotor output in children with cerebral palsy

The first two years of life are critical for the normal development of locomotor circuits. The emergence of independent walking (IW) during this period may reveal how the functional state of neural circuits develops in children with cerebral palsy (CP). In this cross-sectional study, we analysed the activation of eighteen lower limb muscles, corresponding neuromuscular modules, and spinal maps of motoneuron activity in 34 children with CP, in comparison with typically developing (TD) children. Consistency of common modules was used as a criterion for assessing the development of modularity of muscle activity patterns. We found a lack of maturation in children with CP prior to IW, which began late or never. These children exhibited diffused loci of motoneuron activity across lumbosacral segments prior to IW. They also showed two main basic modules, much like newborns, which were augmented to four main modules after IW. The findings indicate that, for IW, the developing spinal circuitry necessitates a differentiation of proximal and distal extensor activity, and an increase in the number of neuromuscular modules under the influence of corticospinal inputs. Early impairments in CP involve conservation of low dimensional control of locomotor movements until IW, suggesting a complex interplay between the maturation of neuromuscular modules and locomotor experience during a critical period of development.