Eligibility Criteria:
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.