Improving Hand Movement Training Through Electrical Stimulation of the Brain

This study will determine if applying electrical stimulation of the brain can influence training to perform finger movements. The study may provide information that can be used to design rehabilitation therapies for people who have lost the ability to move a part of their body, such as an arm, leg, or hand following a stroke. Healthy volunteers 18-50 years of age may be eligible for this study. Candidates are screened with a medical history, physical examination, MRI (if one has not been done within the last year), questionnaire to evaluate memory and attention and a pregnancy test for women who can become pregnant. Participants have the following tests and procedures in seven sessions over about 8 weeks: * Questionnaires to test attention, fatigue and mood before, during and after each session * Surface electromyography: Electrodes are filed with a conductive gel and taped to the skin over one small hand muscle to measure the electrical activity of muscles. * Transcranial magnetic stimulation: A wire coil is held on the scalp. A brief electrical current passes through the coil to stimulate the brain. During the stimulation, the subject may be asked to tense certain muscles slightly or perform other simple actions. The stimulation may cause a twitch in muscles of the face, arm, or leg, and the subject may hear a click and feel a pulling sensation on the skin under the coil. * Transcranial direct stimulation (tDCS) before and during motor training: Small, wet sponge electrodes are applied to the head - one above the eye and the other on the back of the head. A small electrical current is passed between them. The subject may feel an itching or tingling sensation under the electrodes or see light flashes. * Motor learning under tDCS: tDCS is repeated while the subject performs the training task. The training task consists of performing voluntary brisk thumb movements in a direction opposite to TMS-induced movement directions, during 30 minutes. Training blocks are i