Effect of Electrical Stimulation (DC Polarization) to the Brain on Memory

This study will test the effect of direct current (DC) brain polarization (the application of a very weak electrical current to the brain) on learning and memory. Earlier studies have shown that DC polarization can temporarily improve the ability of healthy people to think of certain words. This study will explore whether it can also temporarily improve learning and memory. Healthy people 18 years of age and older may be eligible for this study. Subjects participate in two experimental sessions at the NIH Clinical Center. The first session lasts about 1 hour; the second session, on the next day, takes about 10 minutes. At the beginning of the first session, electrodes are placed on the subject's head and arm for brain stimulation. The current may be turned on for 25 minutes, or only very briefly (sham stimulation). Subjects are not told which type of stimulation they are receiving. No stimulation is applied in the second session. During the sessions subjects are asked to complete the following tasks that will help elucidate the effects of polarization: * Read a list of words and remember them. Later they will try to repeat the words from memory. * Look at a series of designs and remember them. Later they will try to draw the designs from memory. * Push a button on a keyboard when they see a specific item (for example, when the number 7 appears). * Generate as many words as they can think of that begin with a particular letter of the alphabet. Subjects may be videotaped for some or all of the time during the sessions.