1. Implicit learning is a form of procedural learning indicated by behavioral improvement without awareness of a repeated stimulus structure that leads to improved performance. This type of learning has been associated with activation of the primary motor cortex (M1) in neuroimaging studies. While neuroimaging studies contributed to identify this region, they do not provide information about its relative role in the process of implicit learning. Is activity in this region necessary for implicit learning to occur? Is it possible that "energizing" this region using subthreshold transcranial magnetic stimulation can accelerate the implicit phase of learning? The purpose of this protocol is to transiently stimulate focally M1 and dorsolateral prefrontal cortex during acquisition of implicit learning and evaluate the effects on reaction times and accuracy of performance. We plan to study a group of normal volunteers, and three groups of patients who demonstrate impaired visuomotor procedural learning tasks: those with Parkinson's disease, cerebellar disease, and focal frontal lesions. The result expected from this study is an advanced understanding of the role that the motor cortex and dorsolateral prefrontal cortex plays in implicit learning in health and disease. Additionally, we expect to be able to shorten the implicit phase of learning by rTMS particularly in the patient groups that exhibit abnormal procedural learning.