The purpose of this research is to better understand how dementia affects activity in different parts of the brain.

This study is being done to examine the usefulness of Positron Emission Tomography (PET) imaging with florbetapir F 18 as a biomarker in the identification of amyloid-ß peptide (Aß) in the brain. Amyloid-ß peptide (Aß) accumulates in the brains of patients with Alzheimer's disease. Florbetapir F 18 sticks to the amyloid plaques in the brain and emits a low level of gamma rays which can be detected by a PET camera. The development of biomarker and imaging studies that track the development of PPA and reflect the change in people's bodies may help other people who have a similar medical problem in the future.

Inclusion Criteria:

• Subjects who, in the opinion of the investigator, can tolerate the PET scan procedures

Exclusion Criteria:

• Clinically significant cardiovascular disease
• clinically significant hepatic, renal, pulmonary, metabolic, or endocrine disturbances
• Pregnant
• Breastfeeding
• Women of childbearing potential who are not surgically sterile, not refraining from sexual activity or not using reliable methods of contraception.
• History of relevant severe drug allergy or hypersensitivity
• Patients who have received an investigational medication under an FDA Investigational New Drug (IND) protocol within the last 30 days.

Participants will be recruited from other research projects at Northwestern's Mesulam Center. Some of these projects recruit participants from the local Chicagoland area and others recruit participants from across the United States.