Disruption of motor network connectivity post-stroke and its noninvasive neuromodulation

Purpose of review We review the latest evidence for the neural underpinnings of hand motor function recovery after stroke with particular emphasis on how the latter can be enhanced by noninvasive brain stimulation techniques such as repetitive transcranial magnetic stimulation (rTMS) or transcranial direct current stimulation (tDCS). Recent findings New data from longitudinal studies in which rTMS of the lesioned or contralesional motor cortex was combined with motor training showed ambiguous effects: some patients improved whereas others did not show any rTMS effect (compared with control stimulation). In contrast, novel studies using tDCS point to a more consistent effect on distal upper limb function, especially for inhibitory (cathodal) tDCS applied over contralesional M1. Neuroimaging data reveal that the effects of rTMS/tDCS on the functional architecture of the motor system depend upon lesion location, degree of impairment and number of treatment sessions. Furthermore, analyses of regional brain activity and motor network connectivity allow prediction of the behavioural effects of brain stimulation. Summary rTMS and tDCS can be used to modulate stroke-induced changes of motor network activity and connectivity thereby improving hand motor function. The interindividual variability in response to brain stimulation calls for the identification of treatment-associated surrogate markers, which may be provided by neuroimaging.