Each subject will be asked to participate in 4 sessions, at least a week apart. The experiment will test simple reaction times in the thumb or wrist of the paretic hand before and 7 minutes after either genuine or sham TBS. This will be followed by a measure of motor learning, using a well-characterized paradigm (Muellbacher 2001), which involves optimizing an externally paced ballistic thumb (or wrist) movement, and TMS measurement of corticospinal excitability. Performance of the learned task will be further assessed (and TMS measures made) at 2 hours, 1 day and 1 week following the training session. The experimental design for the four sessions will be 2x2 with TBS/sham and Carbidopa-Levodopa/placebo. For TBS, the patient will be given 3 minutes of either genuine or sham TBS to the hand representation of the motor cortex (Huang 2005). For Carbidopa-Levodopa/placebo, identical preparations from the NIH pharmacy will be given 1 hour beforehand. TBS has previously been used in 72 healthy subjects (7 studies) in Europe and in 10 patients with chronic stroke (2 studies) in the Lead Associate Investigator's lab in London. No side effects or seizures have been reported. Ten normal volunteers will be studied first to optimize experimental settings.