Researchers have discovered how the brain can suppress emotionally troubling memories. They say their findings might lead better therapies for patients with post-traumatic stress disorder or anxiety to gain control of debilitating memories.

“You’re shutting down parts of the brain that are responsible for supporting memories,” says Brendan Depue, at the University of Colorado, US. He said his team discovered that activity in the brain’s emotional centre is also reduced.

In the study, published in Science, 16 adult volunteers learned to associate pictures of specific human faces with disturbing pictures, such as car crashes, wounded soldiers, an electric chair or a violent crime scene.

They were then shown each face a dozen times and asked to try and either remember or forget the troubling image associated with each one. After subjects had worked to block a particular negative image, they were shown the associated face one last time, and 53% of the time they could no longer name its troubling pair. Those asked to remember the image, recalled it 71% of the time in the final test.


Reduced activity

The researchers used functional magnetic resonance imaging (fMRI) to show the volunteer’s brain activity in real time.

As the subjects focused on forgetting the images, the team found increased activity in parts of the prefrontal cortex – the brain’s control centre for complex thoughts and actions.

This seemed to direct a decrease of activity in the visual cortex, where images are usually processed. This was followed by reduced activity on the hippocampus, where memories are formed and retrieved, and the amygdala, the emotion hub.

The research is still far from being translated to clinical therapies, Depue and others acknowledge.

“In the first place, the stimuli used in this study may be unpleasant, but they are hardly traumatic,” says John Kihlstrom, at University of California, Berkeley, US, who was not involved in the study.

Harrowing experience

“My prediction is it won’t be as easy to suppress something that’s long-standing and personally emotional,” says Depue. People with post-traumatic stress disorder are often troubled for decades by recurring images of a harrowing experience.

“It might be the case that people with memory disturbances have to gain some control over the memory representation by remembering it and trying a different emotional response to the memory before successful suppression,” he adds.

A drug targeting specific brain regions might eventually boost the ability to suppress, said John Gabrieli, at the Massachusetts Institute of Technology, Cambridge, US.

For a mother haunted by the memory of her son’s suicide, he said, “it is hard to imagine that you would ever get her to forget that the event occurred. But the more you could weaken the memory in any dimension, the better it would be.”

Journal reference: Science (vol 317, p 215)