Network Disorders after Stroke: New Aspects from Functional Magnetic Resonance Imaging

The sensorimotor system comprises a network of cortical and subcortical areas which interact by means of excitatory or inhibitory circuits finally leading to motor output. The balance within this network may be critically disturbed following stroke if the lesion either directly affects any of these areas or damages white matter fibres connecting critical regions. Such effects can be detected by means of functional neuroimaging techniques like positron emission tomography (PET) or functional magnetic resonance imaging (fMRI) and analyses of connectivity. Estimating effective connectivity by means of dynamic causal modelling (DCM) reveals that, after stroke, changes in both intra- and interhemispheric interactions among cortical regions constitute an important pathophysiological aspect of motor impairment in stroke patients. Such disturbances can be partially corrected by non-invasive brain stimulation approaches. Likewise, stimulating noradrenergic mechanisms may also induce a rearrangement of the functional network architecture of the sensorimotor system, which might be useful in a rehabilitative setting with stroke patients. In summary, analyses of effective connectivity may further our understanding of the pathophysiology underlying motor symptoms after stroke, and may help to design hypothesis-driven treatment strategies to support recovery of motor function in patients