This study is recruiting both men and women, but will have a larger proportion of women enrolled as they experience a more significant change in hormones throughout their lives. The women enrolled will be divided into five different categories for data analysis:

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• Pre-menopausal women

• Peri/menopausal women taking horomone replacement therapy (HRT)

• Peri/menopausal women not taking HRT

• Post-menopausal women taking HRT

• Post-menopausal women not taking HRT

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To be eligible for this study, you must meet the following criteria:

• Age 45-85 years

• Have a healthy blood pressure or controlled high blood pressure

• Self-reported normal cognition, subjective memory complaints, or diagnosis of Mild Cognitive Impairment (MCI) - participants must be able to consent for themselves

• Score of ≥ 15 on telephone MMSE (completed during phone screen)

• Willing to undergo all study procedures

• Willing to fast for eight hours

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You may NOT be eligible if you meet these criteria:

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• Currently in another investigational drug study

• Unable to undergo an LP or MRI for medical reasons (blood thinner, some spine abnormalities, metal implants, etc)

• Residence in a skilled nursing facility

• Are pregnant or nursing

• Any systemic illness or medical condition which would cause difficulty complying with study procedures or consenting for oneself

• Heart failure

• Significant neurological disease, stroke, TBI, or history of significant head trauma

• Untreated Major Depression within 2 years of study enrollment

• History of alcohol or substance abuse or dependence