Additional Study Information: The purpose of this study is to see how safe and well tolerated the study drug BMS-986168 is at different drug amounts and to measure the amount of study drug in your blood and cerebrospinal fluid (CSF) after taking the drug. This study will also measure the effect of the study drug on the amount of extracellular Tau (eTau) in your cerebrospinal fluid, the liquid that is around your brain and in your spinal cord. Tau is a protein that builds up in higher amounts in the brain of patients with Progressive Supranuclear Palsy (PSP) and may be related to worsening of the disease. The study will also determine how your immune system reacts to BMS-986168 and check other areas of health and disease that may be related with the study drug.