Long‐term progressive motor skill training enhances corticospinal excitability for the ipsilateral hemisphere and motor performance of the untrained hand

It is well established that unilateral motor practice can lead to increased performance in the opposite non‐trained hand. Here, we test the hypothesis that progressively increasing task difficulty during long‐term skill training with the dominant right hand increase performance and corticomotor excitability of the left non‐trained hand. Subjects practiced a visuomotor tracking task engaging right digit V for 6 weeks with either progressively increasing task difficulty (PT) or no progression (NPT). Corticospinal excitability (CSE) was evaluated from the resting motor threshold (rMT) and recruitment curve parameters following application of transcranial magnetic stimulation (TMS) to the ipsilateral primary motor cortex (iM1) hotspot of the left abductor digiti minimi muscle (ADM). PT led to significant improvements in left‐hand motor performance immediately after 6 weeks of training (63 ± 18%, P