Evaluate the Effect of Atorvastatin on Cerebrovascular Reactivity in Mild Cognitive Impairment (MCI)

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.