Plasticity of central motor and sensory pathways in a case of unilateral extensive cortical dysplasia: investigation of magnetic resonance imaging, transcranial magnetic stimulation, and short-latency somatosensory evoked potentials.

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.