Bad memories can be supressed
People are able to make themselves forget disturbing images.
People can will themselves to forget traumatic or emotional scenes, researchers have found. When the brain conducts such deletions, brain regions that process vision and emotion go quiet.
Knowing that memories can be consciously suppressed, and the brain areas involved, could point to therapies for people who struggle to forget traumatic experiences, such as those with post-traumatic stress disorder or obsessive-compulsive disorder.
Neuroscientist Brendan Depue, of the University of Colorado at Boulder, wanted to find out what goes wrong in the brains of sufferers of such conditions.
Previous studies have shown that people can suppress memories of words. But to make the test relevant to traumatic memories, Depue's team included an emotional component. They showed volunteers pairs of pictures: one of a face, and one to evoke an emotional response — a car crash, or a wounded person.
Once the subjects had learned to associate the image pairs, they were shown the faces alone, and either told to think of the associated picture or to try not to think about it.
The subjects' brains were less active when they deliberately tried not to think of the associated picture, the team found. "It looks like these areas of the brain are being shut down," says Depue.
The decline in brain activity shows that subjects probably weren't thinking of something else to prevent the memorized picture from popping into their heads, he adds.
Brain imaging showed that the prefrontal cortex, the brain's decision-making and planning region, oversees this shutdown. First, the cortex dampens activity in regions that process visual information, and then it suppresses areas that process emotion, such as the amygdala.
Tested afterwards, subjects were much less able to remember the associations that they'd been told not to think about. The team report their findings in Science1.
Press pause on trauma
"This really helps add confidence that we're looking at the right systems," says Mike Anderson, a neuroscientist who studies suppressed memory at the University of Oregon in Eugene. People could be trained to prevent traumatic memories from surfacing by "shutting off the replay mechanism", he says.
More than a century after the idea was proposed, there's still a lot of debate about whether memories can be deliberately suppressed. This differs from Freud's still-controversial concept of repressed memory, in which people unconsciously wipe traumatic memories from their minds.
The new study work won't end the debate about whether unconsciously repressed memories exist or not, but can help get to grips with the mechanisms involved, says Depue.
- Depue, B. et al. Science 317, 215-219 (2007).
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