Glutamatergic Adaptation to Stress as a Mechanism for Anhedonia and Treatment Response With Ketamine

The main purpose of this study is to understand the effects of sub-anesthetic ketamine doses on varying functional domains of depression such as anhedonia, decision-making, and emotion processing in subjects diagnosed with Major Depressive Disorder (MDD). The study will evaluate these effects using a combination of questionnaires, neuroimaging techniques, and behavioral tasks. The clinical trial portion will only include subjects with MDD (Major Depressive Disorder). A separate group of healthy controls, n=60, will be invited to only complete a behavioral/interview session and one neuroimaging session.The healthy controls group will not be randomized nor receive any study intervention and will only serve to collect performance baseline measures. The primary aims of this study are to evaluate 1) the glutamate stress response in MDD patients and matched controls by whole-brain imaging, 2) the multi-modal associations between glutamate stress response and neuroimaging and behavioral assessments of motivation and valuation, and 3) the effect of ketamine versus placebo on glutamate stress response in MDD subjects.