Manic depression (also known as bipolar disorder) affects around one person in 50 at some point in their lives. During the manic periods, a person's experience of the world is altered. Manic depression is probably caused by a combination of inherited and environmental factors. The illness can be treated very successfully with lithium, which acts as a mood stabiliser. Alternative treatments are drugs normally used to treat schizophrenia. Little is known about the problems in the brain that cause mania.