The H-ADD coil is placed on the scalp over the left motor cortex. The center of the coil is placed on the scalp with the handle pointing backward and laterally at a 45° angle away from the midline. Thus the current induced in the neural tissue is directed approximately perpendicular to the line of the central sulcus and therefore optimal for activating the corticospinal pathways transsynaptically (Kaneko et al., 1996). With a slightly suprathreshold stimulus intensity, the stimulating H-ADD coil is moved over the left hemisphere to determine the optimal position for eliciting MEPs of maximal amplitudes (the 'hot spot'). The optimal position of the coil is then marked relative to the 'hot spot' to ensure coil placement throughout the experiment. Resting motor threshold is determined to the nearest 1% of the maximum stimulator output and is defined as the minimal stimulus intensity required to produce MEPs of >50 µV in ≥5 of 10 consecutive trials at least 5 sec apart. The H-ADD coil is held in a stable coil holder ,which can be adjusted at different points relative to the 'hot spot' on the scalp.