Magnetic stimulation of motor cortex and nerve roots in children. Maturation of cortico-motoneuronal projections.

Magnetoelectrical stimulation of motor cortex and peripheral nerve roots was used to establish the maturational profiles of central and peripheral nervous system conduction times in normal children in upper and lower extremity muscles. To obtain true central conduction times, not contaminated by variation due to different preinnervational levels, a protocol using stimulation under full muscular relaxation was used. With this protocol clear responses of the upper extremity could be obtained after the first year of life, whereas in the lower extremity they could not be obtained before the fourth year of life. The developmental profile of central conduction times to upper and lower extremity muscles showed an age-dependent acceleration with adult values not being reached before the age of about 10 years. In contrast, peripheral conduction times obtained after cervical or lumbar root stimulation to upper and lower extremities showed a much faster maturational profile, with adult values being reached at about the age of 3 years. The data are discussed in relation to the available literature on neuromorphological development and provide normative values for the understanding of normal development of motor control in children as well as for application of this technique in children with motor disturbances.