Brain blood flow regulation will be measured in response to environmental changes using MRI.

Global brain blood flow decreases with advancing age; however, some adults have accelerated declines in brain blood flow, placing them at a greater risk of cognitive impairment. Similarly, brain reactivity to increased levels of carbon dioxide decreases with age, with a greater decline in adults with vascular risk factors and is impaired in early Alzheimer's disease. Preclinical models suggest that reduced brain blood flow, results in low levels of oxygen regionally. Currently, there are a lack of human studies that investigate the cause or consequence of altered blood flow regulation in the brain.

The research aims are:

1. Determine the impact of vertebral artery hypoplasia (VAH) on brain reactivity to increased levels of carbon dioxide.
2. Determine the impact of VAH on the brain blood flow response to acute low levels of oxygen.

Inclusion Criteria:

• BMI ≤38.5 kg/m2
• Nonsmoker
• Female subjects: postmenopausal
• Currently enrolled in the Wisconsin Alzheimer's Disease Research Clinical Core

Exclusion Criteria:

• Diagnosis of mild cognitive impairment or Alzheimer's disease
• Uncontrolled hypertension
• History or evidence of hepatic disease, hematological disease, or peripheral vascular disease
• Severe kidney injury requiring hemodialysis
• Cardiovascular disease including: severe congestive heart failure, coronary artery disease, ischemic heart disease (stents, coronary artery bypass grafts) and tachycardia
• History of clinically significant ischemic or hemorrhagic stroke, or significant cerebrovascular disease
• History of HIV/AIDS
• Severe untreated obstructive sleep apnea
• History of diabetes with HbA1c greater than 9.5%
• Major neurologic disorders other than dementia (e.g., multiple sclerosis, amyotrophic lateral sclerosis, brain surgery, etc.)
• Current or recent (<1 year) major psychiatric condition (Axis I) or addictive disorders
• Contraindications to MRI

Subjects for this study, will include healthy adults enrolled in the Wisconsin Alzheimer's Disease Research Clinical Core. Both men and women are eligible to participate in this study.