This study will explore what effects, if any, direct current (DC) brain polarization may produce on mental processes, such as attention, reaction time, working memory, speed of information processing and mood or emotional states. In DC brain polarization, a very weak electrical current is applied to the head. This technique has been used for many years on patients and healthy people with no known serious side effects. Studies have shown that DC polarization can temporarily improve people's ability to think of certain words. To determine if DC polarization can be used as a treatment for certain types of brain disorders, its possible effects on mood and other mental abilities must be determined.

Healthy normal volunteers over age 18 may be eligible for this study.

In each of three 1.5-hour sessions scheduled a day apart, participants complete the tasks listed below to determine the effects of polarization. For each session, electrodes are placed on the head, arm, and hand. One set of electrodes is for brain stimulation; the second set is used to measure the amount of skin moisture on the hand. The participants' tasks are to:

• Push a button on a keyboard when they see a specific item.
• Circle a number or make a mark on a line to indicate how much they feel a particular emotion or sensation at that time.
• Answer questions about themselves, or their opinions on certain topics.
• Look at several pictures and say how emotional they think they are.
• Read about an imaginary situation and say what they would do in that situation.
• Choose between decks of cards to try to win money.
• Compare the angles of lines.
• Identify smells, using a scratch and sniff test.
• At the end of the session, say how they are feeling.

Participants are called by phone on the day after each session to see how they are feeling.