Cortical mechanisms of recovery of function after stroke.

Patients who have suffered hemiplegia from stroke may have some spontaneous recovery that is likely due to reorganization within the cerebral cortex. Understanding this physiology should be useful in devising ways to help patients have better improvement. Techniques, such as transcranial magnetic stimulation and neuroimaging with positron emission tomography, can be used to demonstrate the organization of the human motor system and do reveal plastic reorganization in a number of situations. In relation to stroke, the best recoveries are seen when there is preservation of the corticospinal tract from the hemisphere contralateral to the weakness, but it may well be that areas nearby to the normal motor output areas can partially substitute. There is some evidence for increased corticospinal tract activity originating ipsilateral to the hemiplegia in patients, but this may actually be associated with worse recovery. Patterns of use can influence cortical organization and should play a valuable role in rehabilitation. Certain drugs may affect this process either positively or negatively.