A recent report has demonstrated that the contralesional primary motor cortex (M1) inhibited the ipsilesional M1 via an abnormal transcallosal inhibition (TCI) in stroke patients. We studied whether a decreased excitability of the contralesional M1 induced by 1 Hz repetitive transcranial magnetic stimulation (rTMS) caused an improved motor performance of the affected hand in stroke patients by releasing the TCI. We conducted a double-blind study of real versus sham rTMS in stroke patients. After patients had well- performed motor training to minimize the possibility of motor training during the motor measurement, they were randomly assigned to receive a subthreshold rTMS at the contralesional M1 (1 Hz, 25 minutes) or sham stimulation. When compared with sham stimulation, rTMS reduced the amplitude of motor-evoked potentials in contralesional M1 and the TCI duration, and rTMS immediately induced an improvement in pinch acceleration of the affected hand, although a plateau in motor performance had been reached by the previous motor training. This improvement in motor function after rTMS was significantly correlated with a reduced TCI duration. We have demonstrated that a disruption of the TCI by the contralesional M1 virtual lesion caused a paradoxical functional facilitation of the affected hand in stroke patients; this suggests a new neurorehabilitative strategy for stroke patients.
