From the Department of Physiology and Biophysics (M.R.A., D.A., C.V.G., C.W.C.) Department of Pharmacology and Experimental Therapeutics, Photonics Center (C.V.G.), Boston University School of Medicine, Boston, Massachusetts Department of Neurobiology, University of Massachusetts Medical School, Worcester, Massachusetts (J.F., M.A.) Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Boston, Massachusetts (C.W.C.).