A Study to Investigate Evoked Potentials as Markers of Ketamine-induced Cortical Plasticity in Patients With Major Depressive Disorder

Inclusion Criteria:

* Patient must be medically stable
* Patient must meet Diagnostic and Statistical Manual of Mental Disorders - Fourth Edition (DSM-IV) diagnostic criteria for Major Depressive Disorder (MDD), without psychotic features, based upon clinical assessment and confirmed by the Mini International Psychiatric Interview (MINI)
* Patient must have had an inadequate response to at least 2 antidepressants, one of which is in the current episode of depression
* Patient must have an Inventory of Depressive Symptomatology 30-item Clinician-rated (IDS-C30) total score ≥ 34 at Screening and Day -1
* Women must be postmenopausal, surgically sterile, or, if heterosexually active, practicing a highly effective method of birth control
* Men who are heterosexually active with a woman of childbearing potential must agree to use a double barrier method of birth control and to not donate sperm during the study and for 3 months after receiving the last dose of study drug

Exclusion Criteria:

* Patient has current signs and/or symptoms of liver or renal insufficiency; significant cardiac, vascular, pulmonary, gastrointestinal, endocrine, neurologic, hematologic, rheumatologic, or metabolic disturbances
* Patient has a primary DSM-IV diagnosis of current (active) generalized anxiety disorder (GAD), panic disorder, obsessive compulsive disorder (OCD), posttraumatic stress disorder (PTSD), anorexia nervosa, or bulimia nervosa
* Patient has a current diagnosis of bipolar disorder, mental retardation, or cluster b personality disorder (e.g., borderline personality disorders, antisocial personality disorder, etc)
* Patient has a current or prior diagnosis of a psychotic disorder or MDD with psychosis
* Patient has not responded to treatment with electroconvulsive therapy (ECT) in the current episode of depression
* Patient has suicidal ideation with intent to act, or has homicidal ideation/intent, during Screening phase per Investigator's clinical judgment
* Patient has any significant primary sleep disorder