The brain may register sensory information at the cellular level when it is anesthetized, even though it may not remember having received it, suggests a new study published in the April issue of the journal Anesthesiology.
"This study reveals important new information about how anesthesia affects our brains," says Yan Xu, PhD, the lead author and vice chairman for basic sciences in the department of anesthesiology at the University of Pittsburgh School of Medicine.
For the study, researchers exposed 107 rats to a dozen general anesthesia and odor combinations. After the rats recovered from being anesthetized, the researchers observed their reactions to scented beads and monitored their behavior while they searched for hidden odors.
The rats behaved as if they had never been exposed to the smells, say the researchers, but their examination of the rats' brains on a cellular level showed "imprinting" had occurred and indicated the rats no longer recognized the smells as novel. Higher-order sensory processes continue to occur in behaviorally unconscious brains, according to the findings, but that doesn't indicate awareness under general anesthesia.
Dr. Xu notes that the anesthetized brain's ability to receive sensory information and recognize the information as new or familiar, even without remembering receiving it, should lead to a re-evaluation of anesthesia's effects on memory and learning, and a reassessment of how depth of anesthesia should be monitored during surgery.
For example, write researchers, what do surrogate measures in anesthesia monitors indicate if higher-order sensory processing is partially maintained? Will the cellular registration of a novel sensory input under general anesthesia make the learning of the same sensory input more difficult later in an awake state, given that some level of cellular registration has occurred?