Background. Low-frequency repetitive transcranial magnetic stimulation (rTMS) over the unaffected motor cortex may improve motor function of the paretic hand after stroke. However, low-frequency rTMS might adversely affect bimanual movement by decreasing transcallosal function. Objective. The authors investigated whether combined administration of rTMS and transcranial direct current stimulation (tDCS) prevents deterioration of bimanual movement induced by low-frequency rTMS over the unaffected hemisphere. Methods. A total of 27 participants with chronic subcortical stroke were randomly assigned to receive either 1 Hz rTMS over the unaffected hemisphere, anodal tDCS over the affected hemisphere, or a combination of rTMS and tDCS. All patients performed a pinching motor-training task after stimulation. Bimanual movement and transcallosal inhibition (TCI) were evaluated after stimulation. Results. rTMS and rTMS-tDCS enhanced the motor training effect on the paretic hand. rTMS decreased bimanual coordination and reduced TCI from the unaffected to the affected hemisphere (TCI unaff-aff). rTMS-tDCS changed TCI balance of both hemispheres but did not affect bimanual coordination or TCI unaff-aff. The change in bimanual coordination was negatively correlated with TCI unaff-aff. Following stimulation, improvement in the pinch force in the paretic hand was negatively correlated with TCI balance. Conclusions. Inhibitory rTMS over the unaffected hemisphere transiently caused deterioration of bimanual movements for the current task in stroke patients. This short-term decline was prevented by combined administration of low-frequency rTMS over the unaffected hemisphere and anodal tDCS over the affected hemisphere. These responses to bihemispheric stimulation suggest possible caution and opportunities for the rehabilitation of hand function after stroke.
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