The main purpose of the studies presented in this protocol is to investigate the physiology of motor control in health as well as the pathophysiological modifications taking place during disease. To this end, we will investigate changes in regional cerebral blood flow (rCBF) as an index of regional neuronal activity, associated with various motor and sensory tasks using Positron Emission Tomography (PET). The rCBF will be obtained by measuring the distribution of the cerebral radioactivity during emission scans following the intravenous bolus injection of 15O-labeled water. The very short half-life of 15O (2 minutes) allows us to measure rCBF repeatedly under different task conditions (see methodology and experimental procedures). With the comparison between PET scans performed in different conditions, we can detect the specific task-related activated regions. PET images will be coregistered to high resolution Magnetic Resonance Images (MRI) to get more accurate anatomical information regarding the activated areas. The results will be correlated with that from other physiological approaches including Electroencephalography (EEG), Transcranial Magnetic Stimulation (TMS), functional Magnetic Resonance Imaging (fMRI), and Magnetic Resonance Spectroscopy (MRS). These studies should provide new information not only about the executive component of the voluntary movements in humans but also the different organizational aspects of the preparatory processes that control them.