CHICAGO (Reuters) - U.S. researchers have found a drug-free way to block fearful memories, opening up the possibility of new treatment approaches for problems such as post traumatic stress disorder, they reported on Wednesday.

An undated image of the human brain taken through scanning technology. REUTERS/Sage Center for the Study of the Mind, University of California, Santa Barbara/Handout

The findings in people build on studies in rats that showed that reactivating a memory -- by showing people objects that stimulate the fearful memory -- opens up a specific time window in which the memory can be edited before it is stored again.

“Before memories are stored, there is a period where they are susceptible to being disrupted,” said Elizabeth Phelps of New York University, whose study appears in the journal Nature.

Earlier studies have shown that drugs can be used to block fearful memories, but the results were not long lasting.

Phelps and colleagues based their studies on findings in rats that showed that old memories can be changed or reconsolidated, but only during a specific window time after the rat is reminded of the fearful memory.

That window of susceptibility is typically between 10 minutes after re-exposure to the object to 6 hours later, when the memory stored once again in the brain.

The researchers applied these findings to people in a lab setting. First, they created a fearful memory by showing the volunteers a blue square, and then delivering a mild shock.

Once they had created the fear memory, they simply showed a blue square, which reminded them of the fear memory.

The team waited 10 minutes and then started a training period where the volunteers were repeatedly exposed to the blue square without a shock.

Phelps said simply delaying the exposure training so that it falls within a period during which the memory is susceptible to being edited made a lasting difference in the ability to block the fear memory.

A second group that was exposed to the blue square without the 10-minute waiting period, continued to show fear when exposed to the blue square.

When they brought people back a year later, the group that got the training showed no fear response -- tracked by changes in the skin -- when exposed to the blue square, while other volunteers continued to have a fear response.

Phelps said the important aspect of the study is the time window.

“What we think is happening is because we did it at the right time, you are restoring the memory as safe as opposed to just creating a new memory that competes with the old memory,” Phelps said.

She said the findings are the first of their type in humans, and she cautioned that the findings cannot be immediately applied to people with severe anxiety problems, such as post traumatic stress disorder.

“We did a blue square with a mild shock,” she said. “Normal fear memories are way more complex than that.”

But she said, the findings do open up the possibility of new training methods that can be studied to help people overcome difficult memories.

“It’s really exciting for the potential of treating these disorders. It’s just a ways away,” Phelps said.

The study was supported through a grant by the National Institutes of Health’s National Institute of Mental Health.