Long-Lasting Contralateral Motor Cortex Excitability Is Increased by Unilateral Hand Movement That Triggers Electrical Stimulation of Opposite Homologous Muscles

Background/objective. Long-term changes in the motor cortex can be induced by practicing motor tasks with simultaneous application of peripheral nerve stimulation. This combination may augment motor rehabilitation after stroke but has been used primarily during contraction of the affected hand. The authors tested the effect of a right hand movement that electrically stimulated left hand contraction on right motor cortex excitability. Methods. Three tasks were used in 15 healthy subjects-a motor and stimulation task (MS(task)), stimulation only task (S(task)), and motor only task (M(task)). The MS(task) consisted of isometric thumb abduction of the right hand that triggered paired electrical stimulation of the left abductor pollicis brevis (APB) and first dorsal interosseus (FDI) motor points. The S(task) was performed 1 week later and matched the stimulation received in the MS(task). The M(task) was performed as a control. Transcranial magnetic stimulation applied to the right motor cortex assessed corticospinal excitability, short latency intracortical inhibition, and intracortical facilitation of the FDI and APB before, immediately after, and 30 minutes after task performance. Results. Corticospinal excitability increased in the FDI and APB following the MS(task) but not following the S(task) or M(task). The increased excitability present 30 minutes after the MS(task) also correlated with excitability measures recorded 1 week later. Conclusion. A bilateral motor and electrical stimulation task can drive persistent adaptation within the corticospinal system. Hemiplegic subjects who have poor voluntary movement of the affected hand may be able to contract the unaffected hand to activate and train homologous movements.