Plasticity of cortical hand muscle representation in patients with hemifacial spasm.

To investigate interactions between face and hand representations in the human motor cortex, we studied patients with a hemifacial spasm before and after treatment with Botulinum toxin. Focal transcranial magnetic stimulation was used to assess the cortical motor output map of the abductor pollicis brevis muscle (APB) on both sides. Prior to therapy the representation of the APB ipsilateral to the facial muscle contractions (iAPB) was significantly smaller than on the contralateral side. Two weeks after successful therapy, the iAPB output area was significantly enlarged and expanded into the direction of the face representation. The results indicate activity dependent interactions between hand and face representations in the adult human motor cortex.