Altered corticospinal projections to lower limb motoneurons in subjects with cerebral palsy

The projections of cortical neurons activated by transcranial magnetic stimulation to the motoneurons of lower limb muscles were examined in 22 normal subjects and 14 subjects with cerebral palsy (CP). In normal subjects, magnetic stimulation produced strong facilitation of tibialis anterior (TA) motoneurons, but little or no facilitation of soleus (SOL) motoneurons. This differential facilitation of TA and SOL motoneurons was observed at all stimulus sites on the scalp and all stimulus intensities at which responses could be elicited. In subjects with CP, magnetic stimulation produced almost equal facilitation of TA and SOL motoneurons. This could not be explained by differences in the excitability of the respective motoneuron pools. It is postulated that the projections from the motor cortex to spinal motoneurons are altered in CP. These abnormal projections may contribute to the impairment of voluntary movements experienced by these subjects.