Nicotinic Modulation of the Default Network

Inclusion Criteria: * Age 21 through 50. * Did not consume cigarettes, cigarillos, cigars, or other tobacco or nicotine-containing products more than 20 times in lifetime, and did not use any nicotine-containing product at all within the last two years. * Normal or corrected to normal vision (at least 20/80). Exclusion Criteria: * Presence of metal objects in the body, implanted electronic devices, or any other counter indication for MRI. * Claustrophobia. * Major psychiatric disorders including mood, anxiety or psychotic disorders. * Cardiovascular or cerebrovascular disease, such as history of myocardial infarction, heart failure, angina, stroke, severe arrhythmias, or EKG abnormalities. * Kidney or liver disease. * Hypertension (resting systolic BP above 140 or diastolic above 85 mm Hg). * Hypotension (resting systolic BP below 95 or diastolic below 60). * Use of any prescription or over-the-counter drug other than supplements and birth control. * History of or current neurological illnesses, such as stroke, seizures, dementia or organic brain syndrome. * Learning disability, attention deficit disorder, or any other condition that impedes memory and attention. * Glaucoma, organic pyloric stenosis, uremia or renal insufficiency. * Prostatic hypertrophy, bladder neck obstruction or urethral stricture. * Left-handed or ambidextrous. * Pregnant as determined by urine test, or breast-feeding. * History or current diagnosis of drug or alcohol abuse or dependence. * IQ \< 85 as estimated by the WASI vocabulary subtest.