 Studies will be conducted in the Cleveland Clinics General Clinical Research Unit which is an NIH-sponsored unit designed for studies such as this. Subjects will be admitted on the first day of each study sequence, and discharged the subsequent day. Study subjects will arrive at approximately 8:00 AM. Age, weight and height will be determined and prescription medications will be recorded. Subjects will be fitted with sensors for recording respiration, heart rate and brain electrical activity electroencephalogram, or EEG. Treatment administration will start at noon. To avoid potential effects of circadian variation, treatment administration will start at the same time for each study day in each subject. Because the half-life of Ketamine is short t12 10-15 minutes for sedationanesthesia, we expect participating patients to be fully recovered from any potential sedating effects of Ketamine within an hour or two. 