In order to identify abnormalities like nerve cell damage and overall brain shrinkage related to Alzheimer's disease, it is necessary to know what a normal elderly brain should look like. Some parts of the brain vary widely from one individual to the next, while other parts look nearly identical. This map, created by comparing the location of thousands of specific points in many healthy brains, shows which is which. Red indicates a point of high variability, blue reflects places where brains tend to look alike, and green indicates areas in between.