Study of Brain Changes Shaped by Experience

This study will use magnetic resonance imaging (MRI) scans to explore how the brain changes (reorganizes itself) in response to learning and to brain lesions in healthy people and people with various physical disabilities.

Normal volunteers and patients with disabilities including blindness, limb amputation, hemispherectomy (removal of a cerebral hemisphere), and stroke may be eligible for this study. Candidates will be screened with medical and neurological examinations.

Participants will have MRI scans while they lie still or perform certain movements, as instructed. MRI uses a strong magnetic field and radio waves instead of X-rays to show structural and chemical changes in tissues. During the scan, the subject lies on a table in a narrow cylinder containing a magnetic field. He or she can speak with a staff member through an intercom system at all times during the procedure. All participants will first have a scan to show brain structure, which will take about 30 minutes. A second scan will measure blood flow or biochemical concentration and will take from 1 to 2 1/2 hours.

Depending on their disability, patients will participate in one of the following tests:

• Blindness-This will study the ability of blind people to process tactile information.
• Stroke- This will study mechanisms underlying recovery of motor function after stroke. The patient will perform voluntary movements or remain still during the scan.
• Amputation- This will study mechanisms underlying the ability of the brain to reorganize after amputation. The patient will move different parts of the body or remain still during the scan.
• Hemispherectomy- This will study mechanisms underlying the ability of one side of the brain to control movements of both arms. The patient will make different kinds of movements during the scan.

Normal volunteers will participate in one of the following tests:

• Use-dependent plasticity- This will evaluate the effectiveness of amphetamine and placebo in demonstrating brain flexibility. The volunteer will take an amphetamine or placebo (inactive pill) before the scan and then perform a specific exercise using the thumb.
• Motor fatigue- This will study the mechanisms that underlie fatigue, which affect many patients with neurological conditions. The volunteer will contract muscles in the forearm and hand for several minutes until he or she feels fatigue.
• Light deprivation- This will evaluate changes in the brain that occur after light deprivation. The volunteer will remain at rest in the scanner for up to 150 minutes.
• Somatosensory stimulation-This will examine whether stimulation of the wrist can cause changes in hand representation in the part of the brain that controls movement. The volunteer will make hand movements at different times during the test. In addition, mild electric shocks will be delivered to the wrist for up to 2 hours. Although the shock intensity is regulated to avoid pain, there may be some discomfort.