The researchers are trying to gather information and learn more about imaging tests in racially different people who are cognitively normal or have dementia.

Inclusion Criteria:

• Male or female African Americans 30 years of age or older
• Subjects who have completed or are scheduled to undergo the neurological evaluation procedures described below.

Exclusion Criteria:

• Subjects unable to lie down without moving for 20 minutes.
• Women who are pregnant or cannot stop breast feeding for 24 hours.
• Claustrophobic patients unable to tolerate the scans.
• Subjects with a prolonged QT interval (as demonstrated by ECG test) cannot participate in the Tau-PET scans.
• Standard safety exclusionary criteria for MRI such as metallic foreign bodies, pacemaker, etc, since the quantitative PET data analysis is based on anatomic criteria that are established uniquely for each subject by registration to his/her MRI.