Functional recovery after brain infarction: plasticity and neural transplantation.

In the past, little attention has been given to the role of brain plasticity for the long term functional outcome in experimental stroke although there is substantial evidence for plasticity in other experimental models of neurological disorders. Under clinical conditions, functional improvement occurs in most stroke survivors during the initial months after the ischemic incidence. Recent PET studies in stroke patients, investigated two months or later after stroke, indicate a considerable potential for functional plasticity in the adult human cerebral cortex. Research aimed at the identification of the mechanisms underlying functional recovery should be given high priority, particularly with regard to environmental factors and pharmacological interventions. Pilot experiments of environmental enrichment significantly improved the functional outcome of laboratory animals after brain infarction. Fetal neocortical tissue grafted into the infarcted area in adult rats received afferent fibres from the intact brain and responded to contralateral sensory stimulation with increased metabolic activity, indicating functional integration between neocortical grafts and host afferent systems. However, reciprocal connections from the graft to the host tissue were rare, and it remains to be shown whether grafting will be able to restore the complex cortical organization of the infarcted tissue.