Anxiety & Depression Association of America

1. Male or female ages 40-80 years, inclusive 2. Clinical diagnosis of Parkinson's disease, stage 1, 2 or 3 as determined by the Hoehn and Yahr Scale 3. Meet criteria for major depressive disorder (MDD) as determined by the Mini-International Neuropsychiatric Interview (MINI), and at least 15 on the MADRS, which has shown maximum discrimination between depressed and non-depressed PD patients. 4. For women of reproductive potential, use of highly effective contraception for at least 1 month prior to screening and agreement to use such a method during study participation, as well as a negative pregnancy test at screening. 5. Abstinence from drugs of abuse, other than alcohol, cannabis, nicotine and caffeine for the duration of the study. 6. Stated willingness to comply with all study procedures and availability for the duration of the study. 7. Provision of signed and dated informed consent form.

An individual who meets any of the following criteria will be excluded from participation in this study: 1. Presence of Dementia and a Montreal Cognitive Assessment (MoCA) score of less than 18. 2. A primary psychiatric disorder (as determined by the MINI) except for MDD 3. Active suicidal ideation with intent 4. History of substance dependence in the last 2 years 5. Current substance use disorder, except tobacco use disorder 6. Prior clinical psychiatric treatment with ketamine or prior recreational use of ketamine 7. A history of or current significant medical (e.g. cardiovascular, renal), or neurological (e.g. cerebrovascular, seizure, traumatic brain injury) illness other than PD that is unstable and significantly increase their risk and/or might affect the study objectives, as determined by study physicians 8. Uncontrolled hypertension, defined as average blood pressure greater than or equal to 140 mmHg or an average diastolic blood pressure greater than or equal to 90 mmHg among those patients who have hypertension. 9. Orthostatic hypotension (OH) that presents with symptoms sustained longer than a few minutes (e.g., light-headedness, blurred vision, dizziness, weakness, fatigue) or with syncope. OH is defined by a decrease in systolic blood pressure of 20 mm Hg or a decrease in diastolic blood pressure of 10 mm Hg within 3 minutes of standing compared with blood pressure from the sitting position. 10. Inability to provide written informed consent according to the Yale Human Investigation Committee (HIC) guidelines. 11. Any condition or finding that in the judgement of the PI significantly increases risk or significantly reduces the likelihood of benefit from participation in the study. For participation in the PET/fMRI only: 12. Prior radiation exposure for research purposes within such that participation in this study would place them over FDA limits for annual radiation exposure (5 rem per yr) 13. Contraindications to MRI scanning. 14. Presence of a bleeding disorder as determined by the PT/INR (Prothrombin time and international normalized ratio) test