 This study will examine loss of balance in the elderly. Falls due to balance problems are a major health issue in older people, often resulting in bone fractures and other bodily injuries, and functional decline. In addition, the fear of falling leads some elderly people to restrict their movements and social activities, causing depressed moods and decreased enjoyment of life. Risk factors for falling in the elderly include some standing positions in which older people usually experience balance problems, such as leaning forward or backward. This study will examine these unstable positions and the brain mechanisms associated with loss of balance in the elderly. 