The brain under general anesthesia isn’t "asleep" as surgery patients are often told—it is placed into a state that is a reversible coma, according to three neuroscientists who have published an extensive review of general anesthesia, sleep, and coma in the December 30 issue of the New England Journal of Medicine. This insight and others reported in their review article could eventually lead to new approaches to general anesthesia and improved diagnosis and treatment for sleep abnormalities and emergence from coma.

The researchers explain that a fully anesthetized brain is much closer to the deeply unconscious low-brain activity seen in coma patients, than to a person asleep. Essentially, general anesthesia is a coma that is drug-induced and, as a consequence, reversible. The states operate on different time scales—general anesthesia in minutes to hours, and recovery from coma in hours to months to years, if ever. The study of emergence from general anesthesia and recovery from coma could help to better understand how both processes occur.

Understanding that these states have more in common with each other than differences—that they represent a continuum of activity with common circuit mechanisms being engaged across the different processes of awakening from sleep or emerging from coma or general anesthesia—"is very exciting, because it gives us new ways to understand each of these states," says study coauthor, Dr Nicholas D. Schiff, professor of neurology and neuroscience at Weill Cornell Medical College and a neurologist at New York-Presbyterian Hospital/Weill Cornell Medical Center.

Other coauthors are Dr Emery Brown of Massachusetts General Hospital, Massachusetts Institute of Technology, and Harvard Medical School, and Dr Ralph Lydic from the University of Michigan.

Knowing more about the brain circuit mechanisms may also help researchers develop therapeutic agents to "tweak the circuits as needed, to help us in the areas where we don’t do well, such as abnormalities of sleep and, especially, emergence from a coma," Schiff says.