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Anesthetic Prevents Formation of Painful Memories

April 16, 2008

Researchers at the University of California say low doses of a commonly-used anesthetic could prevent the formation of painful memories.

New Scientist magazine reported that scientists have found that sevoflurane gas stopped patients remembering “emotive” images.

Scans showed the gas interfered with signals between two key areas of the brain.

This could eventually help eradicate rare instances of anesthetized patients remembering the full horrors of their surgery.

Anesthetic drugs are typically used to make patients unconscious before operations. However, their effects on the body are often far more complex.

The researchers in California were investigating the outcome of much lower doses of the gas than those used prior to surgery.

The study treated volunteers either with the anesthetic, or a placebo gas, and then showed them a series of photographs consisting of everyday content, such as a cup of coffee, while others had images designed to provoke more powerful emotional response, such as a bloody severed human hand.

After one week, the volunteers were asked to recall as many of the images as possible.

Volunteers given the dummy gas remembered approximately 29% of the powerful images, and 12% of the others.

But researchers discovered those who had received sevoflurane could remember just 5% of the “emotive” images and 10% of the others.

Brain scans showed that the gas appeared to interfere with impulses between the amygdala and hippocampus, areas of the brain known for their involvement in the processing of emotion and memory.

The researchers reported the discovery of an agent and method for blocking human emotional memory.

They say understanding how drugs could stop this happening might provide clues to “intraoperative awareness”"”rare instances in which the memory-disrupting qualities of anaesthetic drugs fail and patients can recall the experience of undergoing surgery.

While the study suggests that the gas could prevent the acquisition of new memories following painful events, it does not point to any effect on pre-existing memories, good or bad.

According to Dr Anthony Absalom, from Cambridge University, the other anesthetic drugs had been found to interfere with memory formation.

“If a patient is having an uncomfortable or distressing procedure but not a general anesthetic, sedative drugs not only make them more relaxed, but help them not to remember it afterwards,” he said.

Absalom said the same is true in intensive care settings, where patients can spend long periods with tubes into their lungs.

“It is unlikely that anesthetic drugs could interfere with memories that have already been formed,” he added.

But he agreed that it could improve understanding of what happens when patients claim to remember operations even though they have been fully asleep.

“Approximately one in 5,000 patients reports remembering details of operations, and it’s a struggle to understand why – but this kind of research might help,” he said.

The research was published in the journal Proceedings of the National Academy of Sciences.

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