Impaired metabolism and the gene apolipoprotein E (ApoE) are independent risk factors for cognitive impairment and dementia. In humans, there are three major versions of apoE (E): E2, E3, and E4. Some studies suggest that the different versions of apoE have varying effects on whole body and brain metabolism. The goal of this project is to better understand the relationship between apoE and metabolism. This will help investigators identify new targets for the prevention and treatment of cognitive decline and dementia.

The investigator hopes determine whether a participant's version of ApoE affects their metabolic rate at rest and during a cognitive challenge. To determine this, the investigator will measure basal (resting) metabolic rates using a technique called indirect calorimetry (IC). This is accomplished by wearing a loose-fitting face mask that measures oxygen intake and carbon dioxide output.

To more accurately measure the amount of carbohydrates, fats and proteins that the body is metabolizing, participants will be asked to provide two urine samples (one at the beginning, and one at the end, of the study).

To determine what version of ApoE the participant inherited, the investigator will conduct a genetic test on DNA isolated from the participant's blood.

Inclusion Criteria:

• all races/ethnicities
• ages 18-65
• cognitively normal
• good health

Exclusion Criteria:

• pregnant or breastfeeding.
• have a bleeding disorder,
• have a history of stroke, seizures, Parkinson's disease, history of head injury with loss of consciousness, or other dementing disorder.
• have a history of alcoholism or drug abuse
• have a history of schizophrenia or currently suffer from bipolar disorder or major depression.
• have vision or hearing loss severe enough to interfere with cognitive testing

Cognitively normal and are in good overall health.