Anesthesia induces a brain state that more closely resembles a controlled, reversible coma than sleep, according to a new study.

"General anesthesia is pharmacological coma, not sleep," Dr. Nicholas D. Schiff, co-author of the study and the director of the laboratory of cognitive neuromodulation with Weil Cornell Medical College in New York, told Reuters.

In a review article in the New England Journal of Medicine on Dec. 30, Schiff and his colleagues compared clinical signs and electroencephalogram readings of patients under general anesthesia and those simply dozing.

While doctors and their patients often refer to anesthesia as going to sleep, in reality the two states have little in common, the researchers said, with only the deepest phase of sleep and the lightest phase of anesthesia overlapping.

In normal sleep, the brain cycles through various predictable phases, while under anesthesia, the patient is brought to a specific state and kept there for the duration of the procedure. The anesthesia phases brought about for surgery are closest to coma, the doctors said.

Every day in the United States, around 60,000 patients receive general anesthesia for surgery, the researchers said.

Schiff said the findings could be useful in developing models to predict how patients emerge from comas, and even one day developing tools for determining what stage a comatose patient is in.

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