The purposes of this study are to: learn about the safety of the study drug (NBI-98854); learn how subjects tolerate the study drug; and evaluate and compare the pharmacokinetics (PK testing, the study of how the body absorbs, distributes, breaks down and eliminates a drug) of the investigational study drug after taking it alone and with ketoconazole. Ketoconazole is known to affect the PK of many drugs and is studied to more safely prescribe medications.