The purpose of this study is to understand how networks in the brain change over time. Participants will have 2 study visits (about 2 years apart) where they will undergo tests to assess mental function, fill out questionnaires, and undergo a brain MRI. At the first visit only, participants will also undergo a blood draw and a PET scan.
Participants are required to have a Co-Participant accompany them. This individual must be a reliable informant that has contact with the participant at least once per week.