Alzheimer's disease cannot be clinically diagnosed until it begins to lay waste to a person's mind, a vexing reality for those who study it, suffer from it, or care for a loved one. Within a decade, that could change, according to scientists who today released a new definition of the disease. Researchers are on track to develop tests that can identify Alzheimer's in the brain before a loss in memory and reasoning abilities. Better detection could lead to more effective treatment. The new definition, the first since 1984, says that Alzheimer's does not begin with dementia. Instead, it is a long, degenerative process that starts years before symptoms emerge. By redefining the disease, scientists hope to provide a framework to expedite research into the causes and treatment of Alzheimer's.