Department of Anesthesiology, The Third Xiangya Hospital of Central South University, Changsha, Hunan, PR China; Hunan Province Key Laboratory of Brain Homeostasis, Third Xiangya Hospital, Central South University, Changsha, Hunan, PR China. Department of Anesthesiology, The Third Xiangya Hospital of Central South University, Changsha, Hunan, PR China. Geriatric Anesthesia Research Unit, Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, Charlestown, USA. Department of Anesthesiology, The Third Xiangya Hospital of Central South University, Changsha, Hunan, PR China. Electronic address: ouyangwen133@vip.sina.com. Department of Anesthesiology, The Third Xiangya Hospital of Central South University, Changsha, Hunan, PR China; Hunan Province Key Laboratory of Brain Homeostasis, Third Xiangya Hospital, Central South University, Changsha, Hunan, PR China; Center for Experimental Medicine, Third Xiangya Hospital, Central South University, Changsha, Hunan, PR China. Electronic address: jianbintong@csu.edu.cn.