Research shows that recovery from deep anesthesia is not a smooth, linear process but is instead a dynamic journey with specific states of activity the brain must temporarily occupy on the way to full recovery.
"I always found it remarkable that someone can recover from anesthesia, not only that you blink your eyes and can walk around, but you return to being yourself. So if you learned how to do something on Sunday and on Monday, you have surgery, and you wake up and you still know how to do it," says Alexander Proekt, a visiting fellow in Don Pfaff's Laboratory of Neurobiology and Behavior at Rockefeller University and an anesthesiologist at Weill Cornell Medical College. "It seemed like there ought to be some kind of guide or path for the system to follow."
The obvious explanation is that as the anesthetic washes out of the body, electrical activity in the brain gradually returns to its conscious patterns. However, new research by Proekt and colleagues suggests the trip back is not so simple.
In the awake brain, of both humans and rats, neurons generate electrical voltage that oscillates. Many of these oscillations together form a signal that appears as a squiggly line on a recording of brain activity, such as an LFP. When someone is asleep, under anesthesia, or in a coma, these oscillations occur more slowly, or at a low frequency. When he or she is awake, they speed up. The researchers examined the recordings from the rats' brains to figure out how the electrical activity in these regions changed as they moved from anesthetized to awake.
"Recordings from each animal wound up having particular features that spontaneously appeared, suggesting their brain activity was abruptly transitioning through particular states," Hudson says. "We analyzed the probability of a brain jumping from one state to another, and we found that certain states act as hubs through which the brain must pass to continue on its way to consciousness." While the electrical activity in all the rats' brains passed through these hubs, the precise path back to consciousness was not the same each time, the team reports today in the Proceedings of the National Academy of Sciences.
Andrew E. Hudson, Diany Paol Calderon, Donald W. Pfaff and Alex Proekt.Recovery of consciousness is mediated by a network of discrete metastable activity states. Proceedings of the National Academy of Sciences, June 9, 2014 DOI: 10.1073/pnas.1408296111