Transcranial magnetic stimulation (TMS) has been used to describe cortical plasticity after unilateral cerebral lesions. The objective of this study was to find out whether cortical plasticity occurs after bilateral cerebral lesions. We investigated central motor reorganization for the arm and leg muscles in cerebral palsy (CP) patients with bilateral cerebral lesions using TMS. Seventeen patients (12 with spastic diplegia, 1 with spastic hemiplegia, and 4 with athetoid CP) and 10 normal subjects, were studied. On CT/MRI, bilateral periventricular leukomalacia was observed in all spastic patients with preterm birth. In two normal subjects, motor responses were induced in the ipsilateral tibialis anterior, but no responses were induced in any normal subject in the ipsilateral abductor pollicis brevis (APB) or biceps brachii (BB). Ipsilateral responses were more common among CP patients, especially in TMS of the less damaged hemisphere in patients with marked asymmetries in brain damage: in 3 abductor pollicis brevis, in 6 BBs, and in 15 tibialis anteriors. The cortical mapping of the sites of highest excitability demonstrated that the abductor pollicis brevis and BB sites in CP patients were nearly identical to those of the normal subjects. In patients with spastic CP born prematurely, a significant lateral shift was found for the excitability sites for the tibialis anterior. No similar lateral shift was observed in the other CP patients. These findings suggest that ipsilateral motor pathways are reinforced in both spastic and athetoid CP patients, and that a lateral shift of the motor cortical area for the leg muscle may occur in spastic CP patients with preterm birth.

We studied a 13-year-old girl with unilateral extensive cortical dysplasia who had mild hemiparesis with mirror movement and no sensory deficit. Transcranial focal magnetic stimulation (TMS) to the unaffected hemisphere elicited bilateral motor evoked potentials (MEPs) of the abductor pollicis brevis muscle (APB) with similar latency and amplitude. The scalp positions where the MEP amplitudes were highest were at the same site in the unaffected hemisphere for both APBs. TMS to the affected heimsphere showed no MEP for either APB. These data indicated that the APB response of the paretic side originated from the same motor cortex as for the contralateral APB, probably due to axonal sprouting. In the study of short-latency somatosensory evoked potentials, the cortical representation point of the paretic hand sensation was in the ipsilateral unaffected hemisphere; this point was located anterior to the cortical representation point of the contralateral hand sensation. We conclude that reorganization of primary motor and sensory cortex occurs when there is unilateral extensive brain damage in early gestation.

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