Treatment with cholesterol-lowering medications, specifically statins, is associated with up to a 73% reduction in the prevalence of AD, suggesting a potentially promising role for statins in the prevention of AD. In order to better understand the mechanisms through which statins may possibly modify blood AD risk, this study will evaluate whether administration of atorvastatin favorably alters blood flow in the brain (measured by magnetic resonance imaging (MRI)) and blood vessel function (measured by ultrasound).