1. Department of Anesthesiology and Pain Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul 05505, Republic of Korea
2. Biomedical Engineering Research Center, Biosignal Analysis & Perioperative Outcome Research (BAPOR) Laboratory, Asan Institute for Lifesciences, Seoul 05505, Republic of Korea
3. Department of Anesthesiology and Pain Medicine, Brain Korea 21 Project, University of Ulsan College of Medicine, Seoul 05505, Republic of Korea