APOE and Alzheimer disease: Using [11C] Pittsburgh compound B (PIB) -PET to divide cognitively normal subjects into groups based on Aβ (PIB- for low and PIB+ for high Aβ load) as well as ApoE genotype (ApoE ε4- and ApoE ε4+), we explore differences in properties of group metabolic brain networks using FDG-PET for young adults, subgroups of cognitively normal older adults, and patients with Alzheimer's disease.