No Pain, Little Brain: Anesthesia Is More Like Coma Than Sleep

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Every day, some 60,000 patients enter a state more like coma than sleep when they undergo general anesthesia — according to an unsettling study published Dec. 30 in the New England Journal of Medicine.

By exploring the brain regions that are active — or not — when patients are under anesthesia, researchers found more similarities between the brain states of patients in comas and those under general anesthesia than between anesthetized patients and those who were slumbering.

Although doctors like to use the term “going to sleep” when putting patients under anesthesia, the new study finds that the two states are very different, with only the deepest states of sleep resembling the very lightest stages of anesthesia.

In a phone interview with Reuters, study co-author Dr. Nicholas Schiff of Weill Cornell Medical College in New York described the brain under anesthesia:

“The brain is becoming very, very quiet. The activity of the neurons is being dampened dramatically…That is also true in coma.”

Schiff, an expert in coma recovery, said while no two brain injuries are alike, studying the way people come out of anesthesia could be used as a model for predicting the stages of emerging from a coma.

“Although recovery from anesthesia is much faster, there are hints that some of the circuit mechanisms have some overlap,” he said.

The research explains how the return of brain activity after anesthesia follows a predictable pattern as specific brain regions come back online. First, respiration is restored, marking the return of the back of the brain stem. Activity then moves forward in the brain, with salivation, tearing, gagging and grimacing appearing as autonomic functions are restored nerve by nerve, followed ultimately by awareness. The same pattern of awakening may occur more slowly during coma recovery, the authors say. (More on TIME.com: Some Scientific Evidence for Beauty Sleep)

Incidentally, the study also offers some insight into why Michael Jackson might have been so fond of the anesthetic drug propofol — apparently, just before the drug obliterates consciousness, it produces a “state of paradoxical excitation” that may include “euphoria.”

A better understanding of the how anesthesia works may not only help ensure that patients are kept safe and pain-free throughout surgery, but it could also ultimately help improve treatment of coma, and may lead to better solutions for the problems many elderly patients endure during post-surgical recovery.

More on TIME.com:

How to Keep Surgeons From Leaving Things Behind

Oops, my bad! The Scariest Words Your Surgeon Can Say

Do Redheads Really Feel More Pain? The Jury’s Still Out

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