This study will evaluate whether applying electrical stimulation on the cerebellum (posterior and lower part of the brain) can influence brain excitability and hand movement performance.

A new technique became available to stimulate the brain: transcranial direct current stimulation (tDCS), which could improve the ability to learn. Researchers do not know whether applying tDCS over the cerebellum could also influence motor function, and they want to examine changes in brain excitability, by using transcranial magnetic stimulation (TMS).

Patients ages 18 to 40 who are not pregnant may be eligible for this study. They will come to NIH for a medical history and completing a questionnaire about memory and attention. There will be five experiments, each up to 5 hours, for about 1 to 5 weeks, in which patients perform tasks like pinching a special device between the thumb and index fingers, or reaching for target objects on the computer screen. Patients will receive mild electrical stimulation over a different part of the head each day. Some experiments are done without the electrical current, but patients will not know which ones are with or without stimulation. There are also short questionnaires about attention, fatigue, and mood, to be completed before, during, and after each experiment.

Patients will be connected to an electromyography (EMG) machine, to measure electrical activity of muscles. Electrodes are taped to the skin over one small hand muscle. TMS allows electrical pulses to pass through the brain to stimulate it. TMS is used at the beginning of each experiment to determine the precise location on the scalp of two target areas: cerebellum and motor cortex. TMS is a safe procedure. Discomfort, headache, or nausea can occur, but all symptoms usually go away promptly. During motor learning under tDCS, also a safe procedure, patients sit in a comfortable chair, and the arm and wrist and arm are kept still. Sponge electrodes are applied on the chin, back of the head, neck, collarbone, lateral part of the head, or above the eyebrow. A small electrical current is passed between electrodes. Patients may feel an itching or tingling sensation under the electrodes or see slight light flashes. tDCS is applied for 20 to 30 minutes. A magnetic resonance imaging (MRI) scan, which may also be involved, uses a strong magnetic field and radio waves to obtain images of body organs and tissues. Patients lie on a table in a cylinder and may be asked to lie still for up to 60 minutes at a time.

This study will not have a direct benefit for participants. However, knowledge gained may help researchers identify ways to improve movement in people with a brain injury, such as chronic stroke.