The herein established link between chronically elevated plasma cholesterol and the development of memory impairment in aged mice is based on findings, showing that only early exposure to elevated plasma cholesterol (i.e., as evident in ApoE-/- mice already at 4 months of age), indicative of chronic hypercholesterolemia, results in reduced long-term and spatial memory function at an older age (i.e., 12 months of age). This evidence concerns the gene APOE and memory impairment.