Postnatal development of descending motor pathways studied in man by percutaneous stimulation of the motor cortex and the spinal cord.

Using the percutaneous electrical stimulation of the brain and spinal cord, we have determined central motor pathway conduction velocities in a group of 19 healthy fullterm newborns (average post-conceptional age 39.8 weeks) and in 19 infants between 2 months and 8 years of age. The newborns were examined during the first postnatal week. The percutaneous stimulation of the motor cortex and of the cervical and lumbar enlargements of the spinal cord was made by means of bipolar electrodes. The evoked compound muscle action potentials were recorded by bipolar surface electrodes fixed on the skin overlying the thenar eminence muscles and the tibialis anterior muscle. In fullterm newborns, the responses of lower limb muscles to cortical stimulation were more difficult to obtain than those of upper limb muscles. Conduction velocities of central motor fibres along the spinal cord (between vertebrae C7 and L4) were around 10 m/sec in fullterm newborns and 38 m/sec at the age of 4 years. These values are considerably lower than those described for adult man (48-60 m/sec). The adult values are established around the age of 8 years.