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Alzheimer's disease. Conceptual computer artwork of an elderly man with Alzheimer's disease. The image represents the alienation caused by the resulting memory loss and disorientation. The symptoms are caused by the death of brain cells (seen from upper left to lower right). The causes of Alzheimer's are poorly understood, but it is associated with the formation of plaques of insoluble protein (amyloid) in the brain, and decreased levels of the neurotransmitter acetylcholine. Aging is the main risk factor. It is incurable, but the symptoms can be treated with drugs to raise acetylcholine levels. (KEYSTONE/SCIENCE PHOTO LIBRARY/HANS-ULRICH OSTERWALDER)