This study will determine the temporal organization of corticospinal volleys during reach and grasp movements. Multiple descending volleys in the corticospinal tract generate multiple peaks in muscle responses (indirect (I)-waves). I-waves are a mechanism by which corticospinal neurons are transynaptically activated at periodic intervals of ~1.5 ms. This periodic activation contributes to the recruitment of spinal motoneurons and generation of movement. we will use paired-TMS to examine I-waves in surface EMG recordings from upper-limb muscles during reach and grasp movements.