Study Finds Rat Brains Remember Odors While Under General Anesthesia

Posted on March 18, 2014

A new study published in the April issue of Anesthesiology suggests that rat brains may remember odors they were exposed to while deeply anesthetized. Previous research has led to the belief that sensory information is received by the brain under general anesthesia but not perceived by it. The new findings suggest the brain receives sensory information and registers the information at the cellular level while anesthetized.

Rats were exposed to a specific odor while under general anesthesia. Examination of the brain tissue after the rats had recovered from anesthesia revealed evidence of cellular imprinting. However, the rats behaved as if they had never encountered the odor before.

Yan Xu, Ph.D., lead author of the study and vice chairman for basic sciences in the Department of Anesthesiology at the University of Pittsburgh School of Medicine, says in the announcement, "It raises the question of whether our brains are being imprinted during anesthesia in ways we don't recognize because we simply don't remember. The fact that an anesthetized brain can receive sensory information - and distinguish whether that information is novel or familiar during and after anesthesia, even if one does not remember receiving it - suggests a need to re-evaluate how the depth of anesthesia should be measured clinically."

In the experiment 107 rats were randomly assigned to 12 different anesthesia and odor exposure paradigms. Some rats were exposed to the same odor during and after anesthesia, some to air before and an odor after, some to familiar odors and others to novel odors. Some rats were also not exposed to odors at all. After the rats had recovered from the anesthesia, researchers observed their behavior of looking for hidden odors or interacting with scented beads to ascertain their memory of the smell. Researchers then analyzed the rats' brains at a cellular level. The rats had no memory of being exposed to the odor under anesthesia, but changes in the brain tissue on a cellular level suggested the rats "remembered" the exposure to the odor under anesthesia and no longer registered the odor as novel.

Dr. Xu also says, "This study reveals important new information about how anesthesia affects our brains. The results highlight a need for additional research into the effects of general anesthesia on learning and memory."

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