This is a phase 2 clinical trial sponsored by Sage Therapeutics which will examine the safety, tolerability and effectiveness of an investigational drug (Sage-718). For this study we seek to recruit individuals with Parkinson's disease ages 50-75 who are cognitively impaired. This is a rare opportunity to participate in a clinical trial of an investigational drug which is being developed to improve cognition in Parkinson's disease, a symptom of the disease which is rarely studied nowadays. To learn more about the study and whether you are eligible to participate, please email or call the study's coordinator at sandra.skinner@stonybrookmedicine.edu or 631-444-7513.