Despite the fact that general anesthetics have been used since the 1800s, scientists still do not have a thorough understanding of how these powerful drugs work in the brain. In addition to relieving pain and causing loss of consciousness, anesthetics are known to induce amnesia during the surgical period. A recent study has shed light on this aspect of anesthetic action.
Using rats as a research model, Michael T. Alkire, M.D., of the University of California, Irvine, has uncovered the role of the amygdala—a brain region involved in fear, anxiety, and emotion—in memory loss caused by the anesthetic sevoflurane. He placed two groups of rats, one mildly anesthetized and the other untreated, in a lighted chamber facing a dark tunnel. If the rats entered the dark area, an environment rodents prefer, Alkire gave them a brief electrical shock.
The unanesthetized animals remembered this shock until the next day and quickly learned to stay in the safer, lighted environment. However, those treated with sevoflurane behaved differently: Unable to remember the bad experience, these animals continued to enter the tunnel and receive a shock. When Alkire incapacitated the amygdalas of the anesthetized rats, he observed that they could then remember, and avoid, the shock. He concluded that sevoflurane could erase a rat’s memory during the training session, but only if the rodent’s amygdala was working properly.
By pinpointing the amygdala’s role in memory function during anesthesia, this research adds to the growing body of knowledge about how anesthetics exert their effects. It has particular relevance to the relatively rare situations in which patients experience episodes of awareness—and sometimes also pain—during anesthesia, but are unable to move or report the problem. In some people, the experience can trigger post-traumatic stress disorder. A better understanding of how anesthetics interact with the brain to cause amnesia could help reduce or eliminate episodes of awareness. The study also provides new insights into memory formation, especially those related to unpleasant or emotional events.
