Brain molecule may offer key to erasing fearful memories

October 29, 2010

Jon Hamilton

Scientists have discovered a molecule in the brain that may help erase the fearful memories that afflict people with post-traumatic stress disorder.

The substance, described in an online edition of the journal Science, was found in mice. But it's part of a memory system that seems to work the same way in people.

Roger Clem and Richard Huganir of the Johns Hopkins University School of Medicine made the discovery while studying mice conditioned to associate a particular sound with an electric shock.

"If they hear the tone the next day, or even weeks later, the mouse will freeze" because it will bring up the fearful memory of the shock, Huganir tells Shots.

Clem and Huganir wanted to understand how that fearful memory is created.

So they studied the brains of mice that had just gone through fear conditioning. And they noticed that an unusual protein appeared in the amygdala, a part of the brain involved in emotions.

That molecule remained for only a few days and appeared to strengthen the brain circuit responsible for maintaining the fearful memory.

But when the researchers eliminated the protein during this period, mice lost their fearful memory. Forever.

The trick was to eliminate the protein soon after a fearful incident, Huganir says.

"Maybe this is a window of time when behavioral therapy would work much better," Huganir says, adding that it may also be possible to eliminate the protein with drugs.

And he says research on people suggests that it may be possible to create a new window for treatment by having people deliberately recall a fearful memory.

Researchers from New York University found that when people did that, there was a 6-hour window in which the original memory could be altered permanently through behavioral techniques.

Experiments in rodents suggest that's because the molecule involved in fear memories appears once again in the amygdala, Huganir says.

If so, he says, it may be possible to eliminate a person's unwanted memory during the critical period by giving a drug that interferes with the fear molecule. Copyright 2010 National Public Radio.