Inclusion Criteria:  Fluent in English Willingness and ability to comply with scheduled visits, magnetic resonance imaging (MRI) scanning, laboratory tests, and other study procedures. Subjects with well-controlled vascular risk factors, such as treated hypertension, treated hyperlipidemia or well controlled Type II diabetes will be included. Stable medications for at least 30 days. Mini Mental State Exam adjusted for age and education of 25 to 30, inclusive or a Telephone Interview for Cognitive Status score of at least 32 Perform within 1.5 S.D. of age and education matched norms on the Logical Memory Paragraph Delayed Recall Geriatric Depression Scale < 11 Aged 60-85, inclusive Right-handed Reduced vision is allowed if it can be corrected with MRI-goggles  Exclusion Criteria:  Prior known diagnosis of mild cognitive impairment (MCI) or dementia Use of investigational drugs or devices within 60 days prior to screening Subjects with contraindications to MRI cannot participate (i.e., implanted metal including pacemakers, cerebral spinal fluid shunts, aneurysm clips, artificial heart valves, ear implants or metal/foreign objects in the eyes and those with a history of claustrophobia) Pregnant. Major psychiatric disorders such as schizophrenia, schizoaffective disorder, major affective disorder in mid-life, or treatment with electroconvulsive therapy (ECT) (Mild depression that is well treated with stable dose of selective serotonergic reuptake inhibitor (SSRI) antidepressants will be allowed). Have a history of major head trauma defined as a loss of consciousness and/or trauma requiring hospitalization Substance abuse within the past 2 years Active hematological, renal, pulmonary, endocrine or hepatic disorders. Evidence of cortical infarcts or strategically placed lacunar infarct (e.g. dorsal medial nucleus of thalamus). MRI evidence of mild white matter signal abnormalities will be allowed. Active cancer, metabolic encephalopathy, infection Active cardiovascular disease, stroke, congestive or severe heart failure Huntington's disease, hydrocephalus or seizure disorder Cataracts, glaucoma, detached retina's, eye surgery involving the muscles; droopy eyelids, penetrating eye wounds and use of anticholinergic eye drop use Weight equal to or greater than 300 lbs (weight limit of the MRI table). Recurrent vaso-vagal syncopal episodes Unilateral or bilateral vagotomy Severe valvular disorder (i.e. prosthetic valve or hemodynamically relevant valvular diseases) Sick sinus syndrome Hypotension due to autonomic dysfunction