To be enrolled in the study, participants must be between the ages of 18-40 years (younger groups) or 50 years old and older (older groups). The study population will consist of an ethnically diverse sample of approximately 1/3 Caucasian, 1/3 African American and 1/3 Hispanic. Approximately, 25% of participants will be female. The population will consist of veterans with additional recruitment from the community in order to meet project goals.