Results of these aims will be utilized in complimentary modeling approaches and combined with the results of prior studies to provide a comprehensive model of in vivo Aβ kinetics in both the human CNS and periphery. The data and models will be able to confirm and exclude current hypotheses of human Aβ metabolism. The goals of the aims are to determine the CNS Aβ isoform kinetics with a pulse labeling protocol (Aim 1), and to determine the peripheral blood Aβ isoform kinetics with a pulse labeling protocol (Aim 2).