This article first appeared on the College of Liberal Arts Web site.
For a military veteran with post-traumatic stress disorder the sound of a helicopter or airplane could trigger a flashback of bombing raids. A car backfire or any sudden noise could bring back images of a roadside bomb explosion. Even a calm walk in the woods could conjure memories of an ambush in a Vietnam jungle.
But what if there was a way to rewrite those memories? Not erase bad memories altogether -- like in the film "Eternal Sunshine of the Spotless Mind" -- but weaken the intense reactions people feel whenever something reactivates their fears?
In search of a non-invasive way to weaken memories of fear, Marie Monfils, assistant professor of psychology at The University of Texas at Austin, and a team of researchers developed a new technique to tweak a memory-modifying treatment called extinction. Known as "exposure therapy" in clinical settings, extinction involves repeatedly exposing patients to fear stimuli in a safe environment to help them conquer their fears.
Using a protocol called fear conditioning, the researchers first taught rats to associate a tone with a slight electric shock. Subsequently playing the tone without the shock causes the rats to freeze for several seconds when they hear the sound.
To overcome this fear the researchers set off the tone over and over again until the rats no longer anticipated the jolt (a process called extinction). The problem with this technique is that after a time, the fear returns, Monfils said.
That's partly because fear comes from the amygdala, a part of the brain that isn't necessarily logical, Monfils said. It reacts very quickly and sets off the fight-or-flight response. Because fear memories are stored in this particular area of the brain, people have difficulty controlling their reactions to fear stimuli.
The key to diminishing fear's powerful grip on the brain is to capture a resurfacing memory -- of an electric jolt, for instance -- when it is ripe for change. This process, called reconsolidation blockade, occurs when the act of remembering makes the memory weak until it's lodged back into the brain. By combining the strength of extinction and reconsolidation blockade, Monfils found she could update the rats' traumatic memories into less fear-filled ones -- and keep them that way.
Taking advantage of the reconsolidation window, the researchers employed the extinction technique by jogging the rats' memories of shocks by playing a fear-inducing tone just once. After waiting an hour for the reconsolidation window to open, they played the tone over and over to contort the original memory of fear into a memory associated with safety. Monfils found the exposure to the fear stimulus (the tone) during the reconsolidation window seemed to block the fearful memory from returning.
Monfils theorizes that extinction therapy alone creates two memories linked to the fear stimuli, one fearful, one not. Reconsolidation paired with extinction effectively overwrites the original fear memory instead of making a parallel memory, she says.
"Memories are stored in the brain like individual files," Monfils said. "Each time they are opened, they can be modified before they're placed back in storage. Altering a memory during the time it is opened can create an updated memory that can be saved in place of the old one."
The goal of the research isn't to completely erase the memory, because people need to learn and grow from their experiences, she said.
"Memories shouldn't be erased because they are a part of who you are," Monfils said. "If a bad memory interfered with my daily life, I wouldn't want it to be gone forever. I'd rather do something about it by learning how to place it in the right context."
Although neuroscientists and clinicians have many years of research and collaboration ahead of them before the treatment can be used on humans, the finding could lead to a potential drug-free treatment for phobias, panic disorders, PTSD or other anxiety disorders
"We start at a very simple point by studying a basic emotion in basic experiments with rats," Monfils said. "By creating something quite simple, in terms of memory information, it's easier to track it in the brain. And the beauty of working with the rodent model is that we can look at the basic mechanisms of fear with a great degree of precision."