Participation will last up to 6 years. All participants will undergo baseline memory and thinking tests, including a mood assessment and tasks measuring memory and other brain functions. Study staff will conduct a telephone interview with a close family member or friend. Some participants may additionally undergo a 45-minute interview with a clinician, a blood draw, and a computerized tomography (CT) scan. All participants will repeat the baseline memory and thinking tests once annually for 6 years, and some participants will repeat the interview, blood draw, and CT scan at these annual visits as well.