Ever since general anesthesia became available for surgical procedures, doctors were puzzled by the fact that patients can be temporarily rendered completely unresponsive during surgery and then waken with their memories and skills intact. A new study by UCLA researchers has unearthed significant clues regarding the processes whereby normal brains navigate from unconsciousness back to consciousness. It may lead to an increased ability for doctors to predict recovery from a coma or other altered states of consciousness. The findings were published online on June 9 in the Proceedings of the National Academy of Sciences.
A research team led by Dr. Andrew Hudson, an assistant professor in anesthesiology at the David Geffen School of Medicine at UCLA, noted that previous research has found that the anesthetized brain is not “silent” under surgical levels of anesthesia, rather it exhibits certain patterns of activity, which spontaneously changes its activity patterns over time. For the new study, the investigators the electrical activity from several brain areas associated with arousal and consciousness in rats that received the inhaled anesthetic isoflurane. They then slowly decreased the level of anesthesia, as is customarily done with patients in the operating room; they monitored how the electrical activity in the brain changed and searched for common activity patterns across all the rodents.
The investigators found that the brain activity occurred in discrete clumps, or clusters, and that the brain did not uniformly transition between all of the clusters. They found that a small number of activity patterns consistently occurred in the anesthetized rats. The patterns depended on how much anesthesia the rodent was receiving, and the brain would spontaneously transition from one activity pattern to another. As consciousness reemerged, a few activity patterns served as “hubs.” Activity patterns consistent with deeper anesthesia connected to those observed under lighter anesthesia. “Recovery from anesthesia is not simply the result of the anesthetic ‘wearing off,’ but also of the brain finding its way back through a maze of possible activity states to those that allow conscious experience,” explained Dr. Hudson said. He added, “Put simply, the brain reboots itself.”
The study authors note that the study suggests a new way to comprehend the human brain under anesthesia; thus, it could encourage physicians to reexamine how they approach monitoring anesthesia in the operating room. Furthermore, if the results are applicable to other disorders of consciousness, such as coma or minimally conscious states, physicians may be better able to predict functional recovery from brain injuries by assessing the spontaneously-occurring transitions. Dr. Hudson noted that the study also imposes some limitations on theories regarding how the brain returns to consciousness. The next phase of the study will involve the testing of other anesthetic agents to determine whether they produce similar characteristic brain activity patterns with “hub” states. In addition, the researchers hope to better characterize how the brain transitions between patterns.