Inclusion Criteria:  - Research subject conditions that may result in alterations of ventilatory control (capnic status) and balance will be specifically reviewed as criteria for participation.  Exclusion Criteria:  Current pregnancy in women, alcohol use within the past 3 days prior to the experiment, history of balance problems (e.g., vertigo, neuropathy, central or peripheral vestibular disorders), and musculoskeletal disorders affecting the ability to perform a SRT in participants. Patients currently taking carbonic anhydrase inhibitors, opioids, benzodiazepines, hypnotics, first-generation H1 antihistamines, amphetamines, and first-generation antipsychotics. Patients with a history of insomnia, sleep apnea, circadian rhythm disturbances, narcolepsy, movement disorders, chronic low blood pressure, fainting spells, multiple concussions, seizure disorders, migraines, severe headaches and panic attacks. If the patient took medications known to cause prolonged QTc interval and other cardiac arrhythmias, the researchers will exclude the patient from the study.