3. Final recording session is immediately before the second operation as general anesthesia is gradually induced. During this time subjects may be asked to follow simple commands like: "Open your eyes" in order to determine the level of consciousness. Also during this session, if arterial line is placed by the anesthesiologist for real-time blood pressure monitoring we will collect several small (~1 ml) blood samples to determine blood concentration of anesthetics. Approximately 1 teaspoon of blood will be obtained in total. No additional venipuncture will be necessary.