Dopamine Release in Use-Dependent Plasticity in Health and Disease

Detailed Summary

This study will examine how dopamine, a brain chemical, affects motor training. Taken by mouth, dopamine can enhance motor training, especially during rehabilitation after brain damage. The study will also examine whether Sinemet, a drug containing a precursor of dopamine, can improve motor training. Healthy normal volunteers and stroke patients between 18 and 80 years of age may be eligible for this study. Healthy volunteers must be right-handed. Stroke patients must have had a stroke that caused weakness in one hand, from which they have recovered enough to be able to move the thumb in different directions. Participants will have up to three study sessions, as follows: Prestudy 1 (MRI, TMS with motor training) * Session 1: Magnetic resonance imaging (MRI) of the brain. This procedure uses a strong magnetic field and radio waves to show structural and chemical changes in tissues. During the scan, the patient lies on a table in a narrow cylinder containing a magnetic field. He or she can communicate with the staff administering the test at all times. * Session 2: Transcranial magnetic stimulation (TMS) - The subject sits in a comfortable chair with the right forearm held still at the side and the head held still by an aluminum frame. A magnetic coil is placed over the head, and a small probe is attached to the thumb to measure thumb movement. Magnetic pulses are occasionally delivered over the scalp, likely inducing a mild thumb movement. After this test, the subject takes a tablet of either Sinemet or placebo (a look-alike pill with no active ingredient). Fifty minutes after taking the pill, the subject undergoes motor training that involves performing brisk thumb movements at a rate of 1 movement per second. At the end of the training, TMS is repeated. * Session 3: Identical to session 2, except subjects who took Sinemet in session 2 now take placebo, and vice versa. Prestudy 2 (MRI, PET without motor training, no TMS) * Session 1: MRI of the brain if the subject has not had one within the last 12 months. * Session 2: Positron emission tomography (PET) scanning - This procedure provides information on brain chemistry and function. First, the subject is given either Sinemet or placebo. The subject lies on a bed in a doughnut-shaped machine with a custom-molded plastic mask placed over the face and head to support the head and hold it still during the scanning. A catheter (plastic tube) is placed in each arm-one to inject \[11C\]raclopride-a radioactive substance that competes with dopamine for binding in certain parts of the brain and can be detected by the PET scanner-and one to draw blood samples for measuring the level of Sinemet in the blood. * Session 3: Identical to session 2, except subjects who took Sinemet in session 2 now take placebo, and vice versa. Main Study (MRI, TMS, PET with motor training) * Session 1: MRI of the brain, if one has not been done within the last 12 months. * Session 2: TMS, followed by administration of Sinemet or placebo and PET scanning with motor training. The subject lies quietly during the first half of the PET session and performs brisk thumb movements during the second half. After completing the PET scan, the subject undergoes TMS again. * Session 3: Identical to session 2, except subjects who took Sinemet in session 2 now take placebo, and vice versa.

Study Details

Timeline