CLINICAL CORE ABSTRACT This Clinical Core will implement first in human PET imaging with new radiotracers targeting α-synuclein (α-syn) and 4 repeat tau (4R tau). These two types of radiotracers are key for investigation of Parkinson disease (PD) and Multiple Systems Atrophy (MSA), diseases that have α-syn brain pathology, and Progressive Supranuclear Palsy (PSP) and frontotemporal dementias (FTD) that have 4R tau brain pathology. A critical part of these studies is the Clinical Core driven consensus diagnosis conferences to implement careful evaluation of each participant since MSA and PSP can be particularly difficult to diagnose clinically. This represents a critical step for understanding the clinical manifestations of these disorders and for developing new treatments for these and related neurodegenerative diseases.