Biomarker Assessment of Glutamatergic Target Engagement

Inclusion Criteria:

* Age 18-55
* Negative Urine Toxicology
* No present or past psychiatric conditions (including substance abuse or dependence, with the exception of nicotine dependence)
* No family history of schizophrenia in a first-degree relative

Exclusion Criteria:

* Any current DSM IV Axis I disorder and/or past substance abuse of dependence (nicotine dependence is allowed)
* Any current use of amphetamines, opiates, cocaine, sedative-hypnotics, or cannabis
* Current (i.e., within the last 3 months) treatment with any psychotropic medications
* Pregnancy, lactation, or lack of use of effective birth control
* Presence of positive history of significant medical or neurological illness (including any history of seizure), including high blood pressure (SBP \>140, DBP \>90), low blood pressure (SBP \<100, DBP \<60), orthostatic BP change\>20% (1/3 SBP + 2/3 DBP) or cardiac illness or resting heart rate \>100 or \<50
* History of significant violent behavior
* History of recreational ketamine use, recreational PCP use, or an adverse reaction to ketamine. Subjects who have participated prior research ketamine studies will be eligible providing they have participated in no more than 5 previous research ketamine infusions. Subjects can have infusions not more frequently than biweekly and not more than 1/month on average, therefore subjects entering the study will need to wait 1 month if they had a single infusion and 6 weeks if they have had two closely spaced infusions.
* Contraindication to MRI scanning, including metal implants or claustrophobia. Metal implants, pacemaker, other metal (e.g. shrapnel or surgical prostheses) or paramagnetic objects contained within the body which may present a risk to the subject or interfere with the MR scan, as determined in consultation with a neuroradiologist and according to the guidelines set forth in the following reference book commonly used by neuroradiologists: "Guide to MR procedures and metallic objects", F.G. Shellock, Lippincott Williams and Wilkins NY 2001
* Color Blindness