Plasticity and recovery after stoke: Introduction

Abstract

The adult brain retains a capacity for plasticity and functional reorganization throughout the life span and most stroke surviving stroke patients improve to some extent with time. The mechanisms involved may vary with post-ischemic time, type and location of the lesion. Since the time of Hebb more than half a century it is known that environment and experience can enhance neuronal connectivity, and it was long ago proposed that reorganization of cortical representation areas, 'cortical maps', is a neuroanatomical basis for plasticity after stroke (Jenkins and Merzenich, Brain 1987). Nevertheless, surprisingly little research was directed towards brain plasticity after stroke before the last decade. Specific training methods have now been shown to induce cortical reorganization after stroke in humans. On the cellular and molecular level, experimental data indicate that post-ischemic housing in a stimulating (enriched) environment increases the number of dendritic spines, influences gene expression and endogenous stem cell proliferation and/or differentiation. The symposium includes two experimental and two clinical presentations. Mathias Hoehn will present rodent data on in vivo tracing and functional evaluating of exogenous stem cells, and the differentiation and possible integration of the cells as studied with immuno-histochemistry. Anis Mir will up-date how monoclonal antibodies to the neurite growth inhibitory molecule Nogo-A may improve functional after focal brain ischemia, and present evidence that corticospinal and subcortical plasticity may contribute to the beneficial effect. The development of clinical diagnostic and neuroimaging techniques has greatly improved the possibilities for longitudinal studies of the rehabilitation process in humans, and a challenge is how to correlate brain imaging with functional gains. Cathrin Butefisch will review the diagnostic and therapeutic use of transcranial magnetic stimulation, and how the method may be used to elucidate potential mechanisms in brain plasticity. Richard Frackowiak will demonstrate how the dynamic plasticity of cortical maps after stroke can be elucidated with functional MRI, and how changes over time may relate to functional outcome.