LOS ANGELES -- Scientists have found evidence that people can actively suppress disturbing memories by choosing not to think about them, a finding that could lead to improved therapies for post-traumatic stress, whose sufferers are haunted by scary memories they can't control.
By scanning the brains of 16 healthy adults who were shown gruesome photographs, researchers from the University of Colorado discovered that subjects' memory circuits slowed when they were instructed to push mental images of the photos from their minds.
"You can train yourself to remember something, and you can train yourself to forget it," said University of Colorado graduate student Brendan E. Depue, lead author of the study appearing today in Science, a weekly journal published by the American Association for the Advancement of Science.
Massachusetts Institute of Technology neuroscientist John Gabrieli, who was not connected to the research, said the study was a "big step forward."
Previous experiments by Gabrieli and others have shown that subjects can suppress memories of neutral words and images, material viewed as more forgettable than gory scenes or personal trauma.
"The great issues for memory suppression are emotionally intense experiences," Gabrieli said, cautioning that no lab experiment can duplicate the trauma of real military combat or physical abuse.
In the latest experiment, researchers trained test subjects to recognize 40 sets of images, each of which paired an expressionless face with a murder scene, car crash, or other disturbing picture.
After they memorized the pairs, participants were shown only the faces and asked to "think" or "not think" about the corresponding image as a scanner recorded their brain activity.
When subjects were told to block the disturbing image, the scanner recorded reduced activity in the brain regions that process and store memory.
When asked to think about the images, activity in those brain regions increased.
Researchers also conducted the test without the scanner, asking participants to write down whether they remembered or forgot the photo paired with each face.
They were shown each face 12 times.
When subjects tried to block the negative picture, they remembered it 53.2 percent of the time.
But their recall rose to 71.1 percent when they tried to remember the disturbing scene.
Material from Reuters was included in this report.