Reorganization of the human motor cortex by sensory signals: a selective review.

1. The normal human motor cortex can be made to reorganize by repeated stimulation of proprioceptive inputs, with or without concurrent stimulation of the motor cortex by transcranial magnetic nerve stimulation. Appropriate stimulation induces a focal increase in the excitability of corticospinal projections to specific muscles and, possibly, an increase in the area of the cortex projecting to those muscles. 2. We have shown that repeated stimulation on several successive days causes this 'plastic' reorganization to persist for at least several days. We have also used this approach to determine whether increases in the excitability of the motor cortex can be induced in stroke patients (in whom cortical excitability is usually depressed) and whether this is accompanied by functional changes. 3. The results of these studies were mixed but, in patients in whom plastic changes were induced, there were improvements and sometimes marked improvements in both motor function and some electrophysiological parameters. The reasons for the inconsistent results are not clear, but do not appear to relate to the site, size or nature of the lesion.