The purpose of this study is to investigate the effect of newly developed antiepileptic drug, levetiracetam, on cortical excitability in humans. This drug may be useful in patients with myoclonus, and its mode of action is not well understood. We plan to determine if oral administration of levetiracetam in therapeutic dosage alters cortical excitability measured by transcranial magnetic stimulation as well as long-term potentiation measured by pinching practice in humans.