Improvement of Use Dependent Plasticity in Chronic Stroke Patients

This study will examine the role of an amphetamine in improving the effect that electrical nerve stimulation has over brain flexibility associated with motor training in patients who experienced a stroke more than 1 year before. Chronic stroke is the main cause of long-term disability among adults. Previous studies have shown that electrical stimulation given over the skin may improve patients\' recovery of motor function. Furthermore, it is known that amphetamines can improve the effects of sensory stimulation such as touch. Use dependent plasticity refers to a process in which the performance of simple, repetitive finger movements leads to encoding the details of those actions in the primary motor cortex of the brain. Plasticity in this sense refers to the capacity for change in the brain. Patients 18 years of age and older who have had a stroke, who have no history of other neurological and psychiatric illnesses, and who are able to contrite and perform simple attentional tasks and other tasks may be eligible for this study. There will also be healthy participants as a control group. Participants will have an electrocardiogram. They will also go through a practice session of about 3 hours in which they become familiar with the different tasks required in the study: motor training, pinch force, and the Jebsen-Taylor Test-which requires doing as fast as possible actions that include writing, lifting small common objects, turning pages, or lifting light or heavy objects. Then during the study, patients will be involved in a variety of sessions: * Motor training alone for about 3 hours. * Motor training, amphetamine (or placebo), and electrical stimulation for about 6 hours. * Motor training, amphetamine, and no electrical stimulation for about 6 hours. A magnetic resonance imagining (MRI) scan will be done. Patients will lie still on a table that can slide in and out of a metal cylinder surrounded by a strong magnetic field. Scanning time varies from 20 minutes to 3 hours, with most scans lasting between 45 and 90 minutes. Patients may be asked to lie still for up to 60 minutes at a time. As the scanner takes pictures, there will be loud knocking noises, and the patients will wear earplugs to muffle the sound. Patients will be able to communicate with the MRI staff at all times during the scan and may ask to be moved out of the machine at any time. During another procedure called transcranial magnetic stimulation (TMS), a wire coil will be held over the scalp. A brief electrical current will be passed through the coil, creating a magnetic pulse that stimulates the brain. Patients will hear a click and may feel a pulling sensation on the skin under the coil. There may be muscle twitches of the face, arm, or leg. Patients may be asked to tense certain muscles slightly or perform other simple actions so that the coil can be positioned appropriately. The stimulation is usually not painful, although sometimes strong contractions of the scalp muscles can cause discomfort or a headache. Patients can ask to have the procedure discontinued at any time. For the electrical stimulation procedure, three pairs of electrodes will be placed on the skin. A quite brief pulse of current will pass between the electrodes, creating the electrical field that activates the brain. Patients will feel a brief stinging around the electrodes. Regarding the amphetamine, patients will take it orally on up to four different occasions. Usually they will take 10 mg of Dexedrin before testing.