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Alzheimer's disease. Conceptual computer artwork showing the brain of an elderly man affected by Alzheimer's disease. The condition causes the death of brain cells (seen at left). Symptoms include memory loss and disorientation. The causes of Alzheimer's are poorly understood, but it is associated with the formation of plaques of insoluble protein (amyloid, blue) in the brain, and decreased levels of the neurotransmitter (signal molecule) 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)