Alzheimer's disease can begin with a silent decrease in blood flow to the brain. Subtle changes in cerebral blood flow and oxygen consumption are closely associated with hallmarks of the disease, including amyloid plaques and memory-related brain shrinkage. A new study has identified the underlying mechanism for reduced blood flow caused by the amyloid beta protein that accumulates in the brain. This protein causes capillaries in healthy brain tissue to contract, cutting blood flow in half, comparable to the condition in Alzheimer's patients[1]. Reduced blood flow is the first clinically detectable sign of Alzheimer's. A simple, non-invasive scan may one day help detect risk earlier by looking at the brain's vascular health, not just plaques. The research suggests new directions for treatment in the early stages of the disease, as drugs that remove amyloid beta have failed in the later stages[1]. Disorders of blood flow and metabolism appear years before brain damage[6].