Despite their extremely widespread use, anesthetics are actually poorly understood. How the brain recovers consciousness after general anesthesia has mystified scientists and medics for years; after such a significant perturbation, how does the patient wake up with memories and skills unharmed? A new study, published in PNAS, may finally provide us with some answers.
A simplistic theory of how the brain recovers consciousness after anesthesia is that as the anesthetic washes out of the patient, the brain simply follows a steady path toward consciousness. UCLA researchers conducting this study, however, found that this is not the case.
The team administered the anesthetic isoflurane to mice in order to induce unconsciousness and then used electrodes to record brain activity in several regions that are known to be associated with arousal and consciousness. They then gradually reduced the amount of anesthetic and monitored patterns of electrical activity as the rodents slowly returned to consciousness.
While previous research had demonstrated that the brain does exhibit certain patterns of electrical activity under anesthesia, the team discovered that this neuronal activity occurred in discrete clusters. Furthermore, they found that certain patterns of activity were consistently detected in the rodents which were dependent on the amount of anesthetic administered.
En route to recovery of consciousness, the brain was found to transit through several activity states. The brain spontaneously jumped between these patterns of activity, some of which served as “hubs” that connected patterns of activity associated with deeper anesthesia with those associated with lighter anesthesia.
The team note that while many paths through this neuronal network are possible, the brain must pass through these hubs in an orderly fashion to reach consciousness.
“Recovery from anesthesia is not simply the result of the anesthetic ‘wearing off’ but also of the brain finding its way through a maze of possible activity states to those that allow conscious experience,” lead researcher Dr. Andrew Hudson said in a news-release. “Put simply, the brain reboots itself.”
Alongside shedding light on this poorly understood area, this information could have applications in the medical field. For example, if the information can be applied to individuals in a coma then doctors may be able to predict recovery with greater accuracy by examining brain activity in the regions investigated in this study.
The researchers hope to continue this work using other anesthetics to see if the same patterns of brain activity are observed.