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Scientists Erase Specific Memories in Mice

October 21, 2008
HealthDay

It sounds like science fiction, by scientists say it might one day be possible to erase undesirable memories from the brain, selectively and safely.

Using a complex genetic approach, U.S. and Chinese researchers believe they have done just that in mice, but the feat is far from being tested on humans.

Study co-author Joe Z. Tsien, co-director of the Brain & Behavior Discovery Institute at the Medical College of Georgia, Augusta, says the "work reveals a molecular mechanism of how [memory deletion] can be done quickly and without doing damage to brain cells."

The finding is published in the Oct. 23 issue of Neuron.

Humans plagued by painful memories have long wished for a way to eject them from the brain. The concept was the premise of the popular 2004 film Eternal Sunshine of the Spotless Mind, in which two former lovers pay a "memory-erasure" service to expunge the unhappy affair from their minds.

To explore the possibility of safely carving away bits of memory, the study authors first focused on the activity of a common protein found only in the brain, called CaMKII.

In both mice and people, this enzyme is often referred to as the "memory molecule" because of its key role in facilitating brain cell communication -- especially people's ability to learn and retain information.

To hone in on the specific workings of CaMKII, Tsien and his team first developed a "chemical-genetic method" that enabled them to instantly turn the protein "on" or "off" among mice intentionally bred to overproduce the molecule.

After exposing the mice to emotionally powerful stimulations, such as a mild shock to their paws, the scientists then observed how well or poorly the animals subsequently recalled the particular trauma as their brain's expression of CaMKII was manipulated up and down.

When the brain was made to overproduce CaMKII at the exact moment the mouse was prodded to retrieve the traumatic memory, the memory wasn't just blocked, it appeared to be fully erased.

This occurred without impacting the animal's ability to recall any other memories, the scientists say.

A similar observation was made in experiments involving the mice's recognition of specific objects. In those cases, overexpression of CaMKII appeared to eliminate all memory of toys with which the mice had previously been exposed.

According to Tsien, the animal study illustrates how the targeted erasure of specific memories might be genetically triggered in a controlled and harmless manner.

The authors stressed that their work is in its infancy, but they believe it opens up the theoretical possibility of therapeutic applications for humans down the road. Memory erasure might help relieve trauma among people plagued by fearful memories, such as those with post-traumatic stress disorder (PTSD), for example.

"While memories are great teachers and obviously crucial for survival and adaptation, selectively removing incapacitating memories, such as traumatic war memories or an unwanted fear, could help many people live better lives," Tsien said.

However, Dr. Joe Verghese, an associate professor of neurology at the Albert Einstein College of Medicine in New York City, cautioned that the animal work described in the study remains preliminary.

"I think the idea of selectively targeting memory processes is very interesting," he said, "because it not only opens up a whole area of possible intervention but also reveals something about the neurobiology that goes into creating memory in the brain."

"But memory in a human is much more complex than a memory in a mouse," Verghese added. "So, this experimental model, while it brings to mind all sorts of possible applications, is many steps removed from any human application."

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