Dopaminergic Modulation of Frontostriatal Function With a Dopamine Agonist and COMT Inhibitor

Inclusion Criteria: * Age between 18 and 50 years. * Subject is right-handed. * If female, subject is non-lactating, not pregnant, and using a reliable contraception method (i.e. abstinence, intrauterine device (IUD), hormonal birth control or barrier method). * Subject is able to read and speak English. * Subject is a high school graduate. * Subject is able and willing to provide written and informed consent. * Subject is able to understand and follow the instructions of the investigator, and understand all ratings scales. * Subject is in good health. Exclusion Criteria * Using cocaine, stimulants (other than THC, nicotine, \& caffeine)amphetamines, hallucinogens, "ecstasy", opiates, sedatives, pain pills, sleeping pills or other psychoactive drugs within two weeks of the start of the study OR more than 10 times in the last year. * Has a current dependence on, or addiction to any psychoactive drug (except nicotine or caffeine) including alcohol. * Clinically significant medical or psychiatric illness requiring treatment as determined by screening blood tests, medical history, and physical exam performed or reviewed by the study physician. * Subject has a history of major alcohol related complications within the proceeding 2 years (liver failure/cirrhosis, pancreatitis, esophageal varices, etc.) * Liver function test ≥ 3 times normal upper limit. * BAC level \> 0.05% at the beginning of screening visit (within margin of error of detection). * Has a neurological dysfunction or psychiatric disorder. * Has severe low blood pressure. * Has uncontrolled high blood pressure. * Regular use of any of the drugs on the tolcapone or entacapone contraindications list OR within 2 weeks of drug administration. * Regular use of SSRIs. * Has an allergy or intolerance to tolcapone or entacapone. * Subject has received an investigational drug within 30 days of screening visit. * Subject is considered unsuitable for the study in the opinion of the investigator or study physician for any other reason. MRI Exclusion Criteria: * The subject has metal (metal plates, pins, wires or screws, artificial limb, joint replacement or anything that might have been inserted during an operation) in his/her body. * Subject has a pacemaker, defibrillator, stent, or any metal implants related to heart/blood flow problems. * Subject has worked with metals (ie. metallurgy, metal shaving, welding, soldering, etc). * Subject has been wounded with anything metal (bullet, shrapnel or metal filling). * Has ever gotten a piece of metal in the eye. * Has tattoos done with ink containing metal or permanent eyeliner. * Wears color contact lenses. * Has a hearing problem or hearing aid, cochlear implant or past ear surgery. * Has any irremovable dental bridges, dental plates, metal caps or any other non-removable metal in the mouth. * The subject is claustrophobic. * The subject is pregnant. (women only) * Has a IUD. (women only) * Significantly overweight.