This study will examine the effects of direct current (DC) electrical polarization of the brain on thinking speed, reaction time, mood, and brain waves in healthy individuals. The results will provide information for designing further studies to examine the safety and effectiveness of this technique in treating certain brain diseases involving impaired cognition (thought processing). The study consists of three experiments; participants will take part in either one or two of the experiments. Healthy right-handed volunteers between 18 and 80 years of age with 12 or more years of education may be eligible for this study. Candidates will be screened with a medical and educational history and a brief neurological examination. Participants in experiments 2 and 3 will also be screened with a verbal fluency test in which they will be asked to say as many words beginning with certain letters as they can in 1 minute. Participants will undergo the following procedures for the experiment(s) in which they participate: Experiment 1 While resting quietly, subjects receive 20 minutes of weak electrical current stimulation or sham stimulation with no current. For the stimulation, two gauze pads soaked with a conducting salt solution are placed on the head-one on the left side and one above the right eye. The current is passed between the pads and may cause an itching or tingling sensation under the electrodes. Before and after the stimulation, the participant's reaction time-tested by moving a finger as fast as possible at the sound of a tone-and mood are evaluated. Some participants also have an electroencephalogram, or EEG (brain wave recording) during the experiment. After the stimulation, participants take two brief tests of thinking speed, and the mood and reaction time tests are repeated. Experiment 2 The participant sits in a chair with electrodes attached to the muscles that control movement in a finger on the right hand. Reaction time is tested as described in experiment 1. Then, transcranial magnetic stimulation (TMS) is used to test the activity of the brain's motor cortex (the part of the brain that controls movement). For TMS, an insulated wire coil is placed on the subject's scalp. A brief electrical current is passed through the coil, creating a magnetic pulse that travels through the scalp and skull and causes small electrical currents in the brain cortex. The stimulation may cause twitching of the right hand or arm or produce a mild snapping sensation on the scalp. During the stimulation, the electrical activity of muscles in the right hand is recorded on a computer. Following the TMS, DC stimulation is applied, as described in experiment 1. The stimulation begins at a low level and is followed by repeat TMS and DC stimulation at increasingly higher levels. This continues until there is a clear effect on the muscle response to the magnetic pulses, or until the stimulation becomes uncomfortable. At the end of the electrical stimulation, reaction time is tested again. Experiment 3 This experiment uses the average DC level that produced a change in the size of the responses to magnetic stimulation in experiment 2. Thinking speed and reaction time are tested during the DC stimulation, and the mood test is given before and during the stimulation. This test does not use TMS or EEG recording.
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