We will be developing an EEG-based biomarker for the effects of ketamine infusion in patients with Depression. We will be analyzing the effects of ketamine infusion on Depression symptoms and EEG signals.

This trial is a biomarker development study. We will be examining the effects of various doses of ketamine infusion on depressive symptoms and EEG signals in patients with unipolar depression.

Inclusion Criteria:

• Physically healthy patients who meet DMS-5 criteria for a major depressive episode (MDE) in the context of MDD and who score at least 22 on the Montgomery-Åsberg Depression Rating Scale (MADRS)
• If taking antidepressants, dose is stable for at least 6 weeks.

Exclusion Criteria:

• Lifetime history of bipolar disorder, schizoaffective disorder, schizophrenia, or any other psychotic disorder, including MDD with psychotic features
• A first-degree relative with bipolar disorder, schizoaffective disorder, or schizophrenia, with the potential participant younger than 33 years (i.e., still at age of risk for a psychotic disorder)
• Receipt of electroconvulsive therapy within 3 months of enrolling in the study
• History of IV drug use
• Nonresponse or intolerance to ketamine administered either clinically or as part of a prior research study
• Pregnancy, planning to conceive, or sexually active but not using adequate birth control.
• Actively suicidal (CSSRS≥3)
• No antipsychotics or medications (e.g. benzodiazepines, anti-epileptics) that are likely to interact with GABA or glutamate,