Functional imaging correlates of recovery after stroke in humans

The mechanisms that are responsible for the remarkable potential for functi onal recovery from stroke in humans remain unclear, and functional tomograp hic neuroimaging techniques increasingly are being used to investigate this issue. Such studies confirmed that recovery of function is related to the volume of penumbra tissue that escapes infarction. For language, reactivati on of the primary functional areas in the dominant hemisphere is associated with the best prognosis. Evidence for functional plasticity in the immedia te vicinity of infarcts, as demonstrated under experimental conditions with invasive methods, is still limited after stroke in humans, probably becaus e of the limitations of spatial resolution of most currently available meth ods. Often, functional changes in the large-scale networks that support mot or (for example, supplementary and premotor cortex) and language functions (for example, prefrontal cortex) have been found, more extensively after le sions acquired during childhood than at adult age. A frequent finding is an increase in the cerebral blood flow response in corresponding regions of t he healthy hemisphere during unilateral motor activation or language activa tion. It is, however, not yet clear whether that is related to functional r ecovery, and there are several observations indicating that it is often ine fficient. Further systematic follow-up studies and therapeutic intervention trials are needed to clarify these issues.