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Influence of Somatosensory Input on Interhemispheric Interactions in Patients With Chronic Stroke

Background. Ischemia-induced cutaneous anesthesia of the healthy hand in patients with chronic stroke elicits transient improvements of motor performance in the contralateral, paretic hand. Objective. The present study was designed to investigate one of the possible mechanisms underlying this effect. Methods. The authors evaluated the effects of transient ischemic cutaneous anesthesia of the healthy hand (target intervention) and healthy foot (control intervention) on transcranial magnetic stimulation-induced interhemispheric inhibition from the contralesional onto the ipsilesional primary motor cortex (M1). Ten subjects with chronic, predominantly subcortical stroke with motor impairment were assessed. Results. Cutaneous anesthesia of the intact hand but not the intact leg resulted in reduction of the inhibitory drive from the contralesional to the ipsilesional M1 both at rest and immediately preceding movements of the paretic hand. Changes in premovement interhemispheric inhibition showed a trend for correlation with improvements in finger-tapping speed in the paretic hand. Conclusion. The findings suggest that modulation of interhemispheric inhibitory interactions between the contralesional and ipsilesional M1, either primarily or secondary to intrahemispheric excitability changes in either hemisphere, may contribute to performance improvements with cutaneous anesthesia of the intact hand. The present study provides additional insight into the mechanisms by which rehabilitative interventions focused on training one hand and restraining the other may operate after chronic stroke.