Key Takeaways

  • The process of awakening from anesthesia has not been well understood before
  • New evidence shows that when individuals wake from anesthesia, brain dynamics change abruptly, like an “on and off” switch
  • A better understanding of this transition may help prevent side effects of anesthesia

BOSTON – New details have emerged about how the brain recovers from general anesthesia based on research from Massachusetts General Hospital (MGH). The process of awakening from anesthesia has not been well understood before, but studies using microelectrodes directly placed in the cortex of non-human primates now show that when consciousness returns after anesthesia, brain dynamics change abruptly, like an “on and off” switch, despite the fact that the anesthetic concentrations fall gradually. 

A better understanding of how the brain transitions from unconsciousness to consciousness could help lead to better means of preventing side effects of anesthesia.

In this study, researchers trained macaques for a particular task designed to determine alertness and neuronal response to tactile and auditory stimulation. The apes were then anesthetized and tested on those same tasks.  Investigators found that when the primates returned to consciousness it was a “rapid and unstable” process.  There was also significant variation between how individual macaques recovered.

The lead author of the report was Shaun R. Patel, Phd, from the laboratory of Yumiko Ishizawa, MD. The report was published in the February 12 issue of the journal Brain.  

Abrupt state transitions are known to occur during natural sleep as well. Together with research to date, the MGH group’s results suggest that abrupt state transitions are a fundamental manner of how the brain functions. Moreover, they found that losing consciousness and regaining consciousness are not mirror opposites in brain dynamics, rather they are unique processes. 

Transitions of anesthetic-induced unconsciousness and consciousness are accompanied by abrupt changes in the cortical dynamics in non-human primates, and the state transitions do not seem to depend on anesthetic pharmacokinetics. In addition, return of consciousness is not simply an inverse of loss of consciousness, rather, it is a unique process.

About the Massachusetts General Hospital
Massachusetts General Hospital, founded in 1811, is the original and largest teaching hospital of Harvard Medical School. The MGH Research Institute conducts the largest hospital-based research program in the nation, with an annual research budget of more than $1 billion and comprises more than 8,500 researchers working across more than 30 institutes, centers and departments. In August 2019 the MGH was once again named #2 in the nation by U.S. News & World Report in its list of "America’s Best Hospitals."