The investigators are conducting a cross-sectional, observational study to investigate whether plasma GPLD1 concentrations are associated with higher cognitive function and better brain structure and function in two groups of older adults with high or low levels of physical activity.

This is a cross-sectional, observational study which will enroll up to 28 healthy, older adults (65-85 y, BMI 20-35 kg/m2), and stratify by current self-reported physical activity level (equal inactive vs. equal highly active).

Aim 1: Investigate whether physical activity level is associated with GPLD1.

Aim 2: Investigate whether cognitive function and brain structure/function are associated with GPLD1.

Inclusion Criteria:

• Ages 65-85 y (inclusive)
• Body mass index (BMI) of 20-35 kg/m2 (inclusive)
• Willing to have blood and data stored for future research use

Exclusion Criteria:

• History of clinically diagnosed diabetes (Type 1 or 2) or a fasting blood glucose >126 mg/dL
• Diagnosed Alzheimer's disease, dementia, or related-brain diseases
• Chronic use of atypical antipsychotic or bipolar medications
• Initiation of novel pharmacotherapy agents (such as antidepressant, hypertension, or dyslipidemia) within the last 3 months
• Uncontrolled hypertension (blood pressure >160 systolic or >110 diastolic)
• Asthma that limits the ability to participate in moderate to vigorous physical activity or requiring systemic glucocorticoid administration
• Emphysema that limits the ability to participate in moderate to vigorous physical activity or requiring systemic glucocorticoid administration
• Current alcohol use exceeding 14 drinks per week in women, exceeding 21 drinks per week in men, having treatment for alcohol abuse in the last year, or having treatment for alcohol abuse more than 1 year ago (but with inability to refrain from alcohol in the past year)
• Use of illegal drugs or marijuana within 1-month of completing a Screening Visit; treatment for drug addiction in the 1-year or having treatment for drug addiction >1-year ago, but with an inability to refrain from the drug of addiction in the 1-year
• Unwilling to abstain from illegal drugs and marijuana for the duration of the study
• Contraindication for MRI (e.g., metal objects, claustrophobia, etc.)
• Psychotic mental illness (e.g., schizophrenia, bipolar, on-and- off use of anti-psychotic medication)
• History of cardiovascular disease (or diseases of the heart, lungs, or blood) that limits participation in moderate to vigorous physical activity
• History of liver, blood, kidney, thyroid or other diseases that limits moderate to vigorous physical activity at the time of enrollment
• Cancer that limits moderate to vigorous physical activity
• Treatment with systemic immunosuppressant medication
• Taking adrenergic stimulants (e.g., amphetamine) or adrenergic blockers (e.g., Propanolol) that will alter metabolic rate
• Have plans to substantially alter their current level of physical activity over the next 1-month

Up to 28 healthy, older adults (ages 65-85 y, BMI 20-35 kg/m2) stratified by current physical activity level will be enrolled. The investigators will enroll an equal number of inactive adults and an equal number of highly active adults.