Inclusion Criteria:

- Healthy normal volunteers who show no evidence of neurologic deficit on questionnaire
and physical examination

- Females of child-bearing age must be non-pregnant as demonstrated using a pregnancy
test, non-lactating, and must be using adequate contraception or be surgically
sterile

- Age 18 years to 45 years

- Right hand dominant

- High school education or above(to ensure consistent performance on the memory tests
being administered)

- English as native language or equivalent degree of fluency

Exclusion Criteria:

- Any evidence of neurologic deficit including seizures, history of severe head trauma
or any previously or current abnormal study of CNS - (eg. MRI, EEG, etc.)

- Any deficit in auditory or visual ability that would prevent performance of the study
tasks

- History of claustrophobia

- Any history of hypertension (resting BP >150 systolic, >100 diastolic) or taking
anti- hypertensive medication

- Any history of cardiovascular disease including previous myocardial infarction,
arrhythmia, heart valve disease, or cardiac murmur

- Significant pulmonary, renal, gastrointestinal, or endocrine metabolic disease which
in the opinion of the investigator would complicate the goals of this study

- Allergy to propofol, thiopental, eggs or history of acute intermittent porphyria,
history of severe allergic reaction (e.g. anaphylactic shock)

- History of substance abuse

- Currently taking centrally acting medications (benzodiazepines or other anxiolytics,
antidepressants, antipsychotic agents, or agents affecting the cerebral vasculature)

- Any one who is not NPO for at least 6 hours

- Any implant incompatible with MR scanning

- Anyone who, in the opinion of the investigators, would be unwilling or unable to
tolerate the procedures and/or comply with the task instructions

- Body Mass Index (BMI) > 30