Researchers Erased Memories Of Fear In Mice. Could Humans Be Next?

Brilliance | Dec. 11, 2017

Estimates say that 8 percent of the population will experience post-traumatic stress disorder sometime in their lives. The disorder arises after someone has a traumatic experience, like assault, an accident, or the horrors of war. The smallest trigger can often make them feel like they're reliving the trauma all over again.

Certain kinds of therapy can help ease a person's emotional reaction to the memory, but what if sufferers could delete the traumatic memories entirely? That's a potential promise of a new development from a team at University of California Riverside, who claim to have successfully erased memories of fear in mice.

I Will Remember You

The idea of editing memories is all the rage right now. In 2014, researchers successfully prevented triggering events from inducing fear in lab animals by combining drugs that strengthen memory connections with fear-extinction therapy — that is, repeatedly putting the animal in the fear-inducing situation, but without anything scary happening. In 2017, a team from Columbia University found that the brain maintains associative memories (say, a car crash) with a different protein than it uses to maintain non-associative memories (the smell of the fresh-cut grass on the lawn you crashed into), which could lead to drugs designed to weaken triggering memories. But the UC Riverside team appears to be the first to actually pinpoint individual memories and erase them without drugs or therapy.

Eternal Sunshine Of The Lab-Rat Mind

To scrub the memories, they relied on optogenetics, a technique that introduces cells with genes that create light-responsive proteins. Once they're in, researchers can target these individual cells with light to affect their behavior. In the experiment, they took mice that had been genetically modified to let the researchers examine the ways certain neurons connected to form memories in their brains and played them a high and low-pitched tone. But when they played the high-pitched tone, they also gave the mice's feet an electric shock. The mice soon learned to fear the high-pitched tone — when it was played on its own, they froze.

When they examined the mice's brains, they found that the memory connections for the high-pitched tone were much stronger than those for the low-pitched tone. Even after reducing the fear response in some mice by playing the high-pitched tone repeatedly without the shock, those connections remained, showing that fear-extinction therapy may not be a long-term solution for PTSD.

To truly weaken those connections, they used optogenetics to expose the high-pitch connections to low-frequency light. It worked: the mice stopped being fearful of the high-pitched tone.

How applicable this is to humans is an open question, since a lot of what the researchers did can't be done on people. Optogenetics is generally considered unethical for human patients, since it involves injecting a virus to tinker with your genes. But just the fact that it can be done is promising, and could be a first step to a solution for a terrible disorder.

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