Cerebral accumulation of tau and beta-amyloid are major factors of Alzheimer's disease pathology. A novel Positron Emission Tomography (PET) tracer (18-F-AV-1451) now offers the ability to study tau protein deposition in vivo in subjects, in which information on cerebral amyloid deposition has already been gathered. This enables to study effects of tau deposition on neuronal integrity, their relation to effects of beta-amyloid deposition and how this contributes to cognitive impairment or well-being in the elderly.