Detection of Disease-Related Changes in Pre-Symptomatic Alzheimer's Disease

Inclusion Criteria: * Individuals between the ages of 55 and 80 years old (inclusive). * MMSE total score \> 27 * Two risk factors for AD: * Subjective memory complaints. * A positive (suspected) first-degree family history for the disease. * Permitted medications stable for at least 1 month prior to screening. * Subjects may take stable doses of antidepressants lacking significant anticholinergic side effects (do not have a history of major depression within the past year). * Estrogen replacement therapy. * Adequate visual and auditory acuity to allow neuropsychological testing. * Good general health or without any clinically significant abnormalities . * Vitamin supplements (including Vitamin E) will be acceptable. * Subjects must be willing and able to provide written informed consent. Exclusion Criteria: * History of major traumatic brain injury, other known neurologic disease or insult * Mini Mental State Examination (MMSE)total score \< 27 * Regular (daily) use of narcotics or antipsychotic medications * Poorly-controlled major depression or another Axis I psychiatric disorder as described in DSM-IV within the past year. * Psychotic features, agitation or behavioral problems, within the last 3 months. * History of alcohol or substance abuse or dependence within the past 2 years (DSM IV criteria). * History of schizophrenia (DSM IV criteria). * Any significant systemic illness or unstable medical condition which could lead to difficulty complying with the protocol including: * History of systemic cancer within the past 5 years (non-metastatic skin cancers are acceptable). * History of myocardial infarction in the past year or unstable or severe cardiovascular disease including angina or Congestive Heart Failure (CHF) with symptoms at rest. * Clinically significant obstructive pulmonary disease or asthma. * Clinically significant and unstable gastrointestinal disorder within two years. * Insulin-requiring diabetes or uncontrolled diabetes mellitus. * Uncontrolled hypertension (systolic BP \> 170 or diastolic BP \> 100). * History of clinically significant liver disease, coagulopathy, or vitamin K deficiency within the past 2 years. * History of symptoms of narrow-angle glaucoma. * Clinically significant obstructive uropathy * Use of centrally active beta-blockers, narcotics, methyldopa and clonidine within 4 weeks prior to screening. * Use of anti-Parkinsonian medications (e.g., Sinemet, amantadine, bromocriptine, pergolide and selegiline) within 2 months prior to screening. * Use of neuroleptics or narcotic analgesics within 4 weeks prior to screening. * Use of long-acting benzodiazepines or barbiturates within 4 weeks prior to screen. * Use of short-acting anxiolytics or sedative-hypnotics more frequently than 2 times per week within 4 weeks prior to screening (note: sedative agents should not be used within 72 hours of the baseline and follow-up visits. * Initiation or change in dose of an antidepressant lacking significant cholinergic side effects within the 4 weeks prior to screening (use of stable doses of antidepressants for at least 4 weeks prior to screening is acceptable) * Use of systemic corticosteroids within 3 months prior to screening. * Medications with significant cholinergic or anticholinergic side effects within 4 weeks prior to screening. * Use of anti-convulsants within 2 months prior to screening. * Use of warfarin (Coumadin) within 4 weeks prior to screening. * Any prior use of any FDA approved medications for the treatment of Alzheimer's disease (e.g., tacrine, donepezil, or other newly approved medications). * Use of any investigational drugs within 30 days or 5 half-lives, whichever is longer, prior to screening. * Subjects who, in the investigator's opinion, will not comply with study procedures. * Known hypersensitivity to F-18, tropicamide, and/or scopolamine or agents of this class of drugs.