The purpose of this study is to evaluate the effect of atorvastatin on brain vessel reactivity and with it on blood flow in people with mild cognitive impairment.

Participants are first being informed about potential benefits and risks of the study and are required to give written consent. After that participants will undergo detailed phone screen to determine eligibility for study entry. At week 0, participants who meet eligibility requirements will be prescribed atorvastatin (40 mg, once in the evening) in an open-label manner.

Inclusion Criteria are chosen to include participants with MCI, enriched for vascular risk factors:

• MCI defined by Clinical Dementia Rating (CDR) of 0.5 or 1.0.
• Memory, processing speed, executive function, language - cognitive scores > 1.5 standard deviations below age-education norms.
• Not demented by history.
• Not taking statins currently or in the last 6 months.
• Cognitive/functional impairment not likely due to another neurological disease or delirium.

Exclusion Criteria:

• Taking a statin currently or have taken a statin in the last 6 months.
• Contraindications to taking a statin.
• Transplant patient taking cyclosporine.
• Unable to undergo MRI procedures (such as having an implanted pacemaker or defibrillator or stimulator or having non MRI compatible metal).
• Diagnosis of dementia by history.
• Current diagnosis of substance abuse.
• History of stroke or myocardial infarction in past 6 months.
• History of HIV.