This study will assess the efficacy of ketamine for the treatment of depression in Parkinson's disease (PD), in a parallel, double-blind, placebo controlled randomized clinical trial (RCT). Imaging will be used to examine the mechanistic effects of ketamine treatment. Specifically, the investigators will use positron emission tomography (PET) to measure synaptic density and functional magnetic resonance imaging (fMRI) to measure functional connectivity. The investigators hypothesize that a course of ketamine treatment will result in a significant reduction in depression severity compared to placebo. Mechanistically, ketamine will result in a reorganization of functional networks and an increase in synaptic density.
The main purpose of this study is to examine the efficacy and safety of a repeated dosing ketamine infusion paradigm compared to placebo in individuals with PD.~A subset of participants in each arm will undergo baseline and post-treatment PET and fMRI scans, to examine whether changes in synaptic density and reorganization of functional networks underlie ketamine's putative antidepressant effects in PD.