Previous studies have demonstrated that single-pulse transcranial magnetic stimulation (TMS) applied to the primary motor cortex (MI) exerts a transient inhibitory effect on the contralateral MI. Furthermore, down-regulation of excitability in MI of one hemisphere by 1Hz rTMS results in increased excitability in the homologous MI accompanied by performance improvements in simple motor tasks performed by the hand ipsilateral to rTMS. It has been proposed that this phenomenon relies on interhemispheric disinhibition between both MI. Furthermore, interhemispheric disinhibition is also a promising method for boosting neurorehabilitation since interhemispheric disinhibition has been successfully applied in stroke patients to enhance motor cortex excitability and hand function or reduce aphasia. The purpose of this protocol is to test the hypothesis that interhemispheric disinhibition of the left MI by down-regulating activity in the right MI can be further enhanced by additional up-regulation targeting the left MI.