Healthy brain aging is a function of not only the neurons in the brain, but also the blood flow to the brain. Classic characteristics in the brain associated with dementia (including Alzheimer's Disease)  include brain abnormalities (such as amyloid plaques and tau fibril entanglement) and white hyper sensitivities. White hyper sensitivities are shown as white areas in MRI's of the brain, and are believed to be a result of inadequate blood flow to the brain.