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Rewiring the Brain After Stroke

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Science Translational Medicine  29 Sep 2010:
Vol. 2, Issue 51, pp. 51ec151
DOI: 10.1126/scitranslmed.3001731

Stroke is a devastating event that has catastrophic consequences for those who survive. Although much is known about risk factors for stroke, there are few options for the long-term care of stroke patients. Recent work has shown that neural circuits in the brain become reorganized after stroke and that this reorganization could be commandeered clinically to optimize recovery. Important brain regions in this response include the premotor cortex, where planning of complex movements occurs, and the primary motor cortex, which executes these plans through neuronal projections that descend through the corticospinal tract to the spinal cord. Bestmann and colleagues now shed light on the reorganization of these brain regions. They use transcranial magnetic stimulation (TMS) to drive neural circuit reorganization in the brains of stroke patients with different levels of impairment. They find that stimulating the premotor cortex on the side of the brain opposite to the stroke [the contralesional dorsal premotor cortex (cPMd)] affects the primary motor cortex on the side of the brain where the stroke occurred [the ipsilesional primary motor cortex (iM1)] and that this communication between brain hemispheres is altered in those stroke patients exhibiting more clinical impairment. This study suggests that optimizing circuit reorganization in the motor cortex may improve motor activity in stroke patients.

The investigators used paired-coil TMS to evaluate whether stimulating the cPMd in stroke patients would positively regulate the iM1, and whether this effect depended on active muscle activity in a hand weakened by stroke. Stimulation of the cPMd by paired-coil TMS boosted activity in the iM1 motor cortex (measured with functional magnetic resonance imaging), particularly as stroke patients performed a hand grip task. The effect was greatest among those patients who were the most impaired but did not seem to be influenced by the age of the patient, the time elapsed since the stroke, results of the hand grip test, or effects of cPMd stimulation on other brain regions. In contrast, prior work has shown that stimulation of the cPMd in healthy individuals has the opposite effect, resulting in down-regulation of M1 primary motor cortex activity. This suggests that the stroke had already induced some cortical reorganization. The Bestmann et al. study demonstrates how ongoing cortical circuit reorganization after stroke can be translated into clinical interventions that may help in the rehabilitation of stroke patients.

S. Bestmann et al., The role of contralesional dorsal premotor cortex after stroke as studied with concurrent TMS-fMRI. J. Neurosci. 30, 11926–11937 (2010). [Abstract]

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