We therefore plan to study tau pathology measured by 18F-AV-1451 in subjects with already existing data on cerebral amyloid deposition (11C-Pittsburgh Compound C, Flutemetamol). We will be able to relate tau pathology to past and prospective cognitive performance assessed by a detailed neuro¬psychological examination, and we will be able to investigate whether cerebral tau pathology is reflected by peripheral blood biomarkers. For this purpose we will include elderly subjects with various degrees of cognitive performance (cognitively healthy, mild cognitive impairment, dementia) and various degrees of cerebral amyloid deposition (dichotomized or quantitative). We will also include Frontotemporal Lobar Degeneration (FTLD) cases to study tau effects in neurodegenerative disease in the absence of beta-amyloid.