Learning to forget your unhappy past
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Friday, 13 July 2007
They say their findings might lead to a way to help people 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, a neuroscience doctoral student at the University of Colorado who worked on the study.
The concept of memory suppression has been a controversial one among psychologists for a century.
But in this study neuroscientists used brain scans to show that volunteers who have been asked to banish disturbing memories show very specific patterns of brain activity.
Depue and colleagues taught 18 adult volunteers to associate pictures of human faces with pictures of car crashes or wounded soldiers.
They were then shown each face a dozen times and asked to remember or forget the troubling image associated with each one.
When they worked to block a particular negative image, then looked at the face one last time, they could no longer name its troubling pair in about half of the trials, Depue and his colleagues report today in the journal Science.
The researchers used a brain imaging method called functional magnetic resonance imaging, or fMRI, which shows the brain's activity in real time, to track what was going on in the brain and obtained usable data from 16 of the 18 people in the trial.
Several steps in the process
In the test, parts of each volunteer's prefrontal cortex, the brain's control centre for complex thoughts and actions, were activated.
This seemed to direct a decrease of activity in the visual cortex, where images are usually processed.
Then the hippocampus, where memories are formed and retrieved, and amygdala, the emotion hub, were deactivated.
Denpue says that memory suppression may have been an evolutionary advantage, say for Stone Age hunters narrowly escaping death while hunting.
"If the hunter became so beleaguered by memories of that incident that he stopped hunting, then he would have starved to death."
The research is still far from being translated to the psychiatrist's office, Depue and others acknowledge.
"In the first place, the stimuli may be unpleasant, but they are hardly traumatic," says the University of California Berkeley's Professor John Kihlstrom, who was not involved in the study.
"My prediction is it won't be as easy to suppress something that's long-standing and personally emotional," Depue says.
People with post-traumatic stress disorder are often troubled for decades by recurring images of a harrowing experience.
Still, patients might practice blocking such memories out of their minds, or at least reducing their emotional sting.
"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," Depue says.