Exploration of the hypothesis that general anesthesia is not a singular threshold but is a continuum of central nervous system depression dependent on interpretation of nociceptive stimuli.

Inclusion Criteria:

• American Society of Anesthesia (ASA) classification score I-II male and female volunteers
• Normal healthy individual by medical history and physical examination
• Uncomplicated airway anatomy
• Body Mass Index (BMI) between 18-29
• Subject willing to give consent and comply with evaluation and treatment schedule
• 18-55 years of age (inclusive)
• Negative durg screen for marijuana, cocaine, ecstasy, phencyclidine (PCP), amphetamines, benzodiazepines, opiates and methamphetamines
• Woman of childbearing age byst be utilizing reliable means of contraception
• Able to read, speak and understand English

Exclusion Criteria:

• Physical of psychological condition which would impair study participation as determined by the principal investigator
• Known or suspected neurological pathologies as assessed by the principal investigator
• History of significant alcohol or drug abuse, a history of allergy to opioids or propofol, or a history of chronic drug requirement or medical illness that is known to alter pharmacokinetics or pharmacodynamics of fentanyl and/or propofol
• Known or suspected hypersensitivity to any study drug
• Taken any medication within 2 days prior to study drug administration, with the exception of oral contraceptives
• Baseline tolerance above 50 mA on TES
• Pregnancy or lactation
• Consumed food within 8 hours or liquids within 4 hours prior to study drug administration
• Participation in any other investigational device or durg study within 30 days of enrollment
• Diagnosis of sleep apnea
• Current prescription to anti-depressant or anti-anxiety medication