Reorganization of cerebral networks after stroke: new insights from neuroimaging with connectivity approaches
The motor system comprises a network of cortical and subcortical areas interacting via excitatory and inhibitory circuits, thereby governing motor behaviour. The balance within the motor network may be critically disturbed after stroke when the lesion either directly affects any of these areas or damages-related white matter tracts. A growing body of evidence suggests that abnormal interactions among cortical regions remote from the ischaemic lesion might also contribute to the motor impairment after stroke. Such disease-induced changes can be investigated non-invasively by applying models of connectivity onto fMRI data aquired in stroke patients. Based on such data, I suggest that pathological intra- and inter-hemispheric interactions among key motor regions constitute an important patho-physiological aspect of motor impairment after subcortical stroke. I will also demonstrate that therapeutic interventions, such as repetitive transcranial magnetic stimulation, which aims to interfere with abnormal cortical activity, may correct pathological connectivity not only at the stimulation site but also among distant brain regions. In summary, analyses of connectivity further our understanding of the pathophysiology underlying motor symptoms after stroke, and may thus help to design hypothesis-driven treatment strategies to promote recovery of motor function in patients.