The patterns of spontaneous activity in the brain, recorded with multiple electrodes, change as the concentration of the anesthetic isoflurane is decreased (bottom panel), until the animal recovers consciousness (indicated by “ROC”). Each panel shows the power in a different brain region as a function of frequency over time. Red indicates high power and blue indicates low power. The patterns of brain activity change abruptly over time, and some patterns are present at several concentrations of anesthetic.
One of the mysteries of anesthesia is how patients can be rendered unresponsive during surgery and then wake up with all their memories and skills intact. A UCLA study provides new clues that illuminate how our brains transit from unconsciousness back to consciousness.
Previous research has shown that the anesthetized brain is not “silent” under surgical levels of anesthesia but experiences certain patterns of activity, and it spontaneously changes its activity patterns over time, says Andrew E. Hudson, MD, PhD, assistant professor of anesthesiology. Using an anesthetized rodent model, Dr. Hudson and his research team recorded the brain’s electrical activity by placing electrodes in several areas associated with arousal and consciousness. They then slowly decreased the amount of anesthesia, as is done with patients in the operating room, monitoring how the electrical activity in the brain changed and looking for common activity patterns across all the study subjects.
The researchers found that the brain activity occurred in discrete clumps, or clusters, and that the brain did not jump among all of the clusters uniformly. A small number of activity patterns consistently occurred in the anesthetized rodents, depending on how much anesthesia the subject was receiving, jumping spontaneously from one pattern to another. A few activity patterns served as “hubs” on the way back to consciousness, connecting activity patterns consistent with deeper anesthesia 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,” Dr. Hudson says. “Put simply, the brain reboots itself.”
The study suggests a new way to think about the human brain under anesthesia and could encourage physicians to re-examine how they approach monitoring anesthesia in the operating room. Additionally, if the results are applicable to other disorders of consciousness — such as coma or minimally conscious states — doctors may be better able to predict functional recovery from brain injuries by looking at the spontaneously occurring jumps in brain activity.
The UCLA researchers will next test using different anesthetic agents to determine if they produce similar characteristic brain activity patterns with “hub” states. They also hope to better characterize how the brain jumps between patterns.
“Recovery of consciousness is mediated by a network of discrete metastable activity states,” Proceedings of the National Academy of Sciences, June 24, 2014