DENVER—Even the originator of the concept of repressed memories, Sigmund Freud, abandoned it in his latest years. But a study by University of Colorado researchers, published this week in Science magazine, suggests people are at least capable of suppressing unpleasant thoughts by “shutting down specific portions of the brain.”
More than 100 years after Freud’s death, scientists remain divided over whether repressed or suppressed memories really exist. Some plaintiffs in court cases won large settlements based on the concept before many studies questioned its validity.
CU researchers repeatedly exposed test subjects to violent and nonviolent images and later asked them to recall them. The rate of recall dropped after the subjects were asked not to think about the violent images, researchers said.
“These results indicate memory suppression does occur, and, at least in nonpsychiatric populations, is under the control of prefrontal regions (of the brain),” the authors wrote in Science.
Dr. Doug Bremer, professor of psychiatry and radiology at Emory University School of Medicine in Atlanta, said the study had important implications “for areas such as alterations in traumatic memories and delayed recall of childhood abuse, as well as post-traumatic stress disorder.”
Sixteen people with no signs of psychological problems participated in the study by Brendan E. Depue, a doctoral candidate in neuroscience, CU associate psychology professor Tim Curran and professor Marie T. Banich.
The subjects were repeatedly shown 40 pairs of images. Each pair included one negative object such as a car accident, violent crime scene, electric chair or battlefield scene, accompanied by a neutral human face.
Then, while being monitored by a functional Magnetic Resonance Imaging scanner that can detect neural activity, they were shown the same pairs of images while wearing goggles that screened out the violent images.
Depue said the subjects were questioned twice about the images. In one series of questions they were told to think about the violent images; in the other they were told not to think about them.
When they were told to recall the violent images, 71.1 percent of the violent images were remembered. When they were told not to think of them, 53.2 percent were remembered.
“Even though it is a small difference it is highly significant,” said Depue. “There is enough of a difference to know that the brain is instituting cognitive control that suppresses the violent memories.”
Repetition may be key to possible suppression of unwanted memories, the study suggests.
“Our data also provide an intriguing hint that, as suggested in clinical practice, it is necessary to ‘revisit’ an emotionally distressing memory before it can be controlled,” Depue said.
Much more study is needed to determine whether patients with post-traumatic stress disorder or other reactions to trauma could benefit from the findings, Depue said.
“We have shown in this study that individuals have the ability to suppress specific memories at a particular moment in time through repeated practice,” Depue said. “We think we now have a grasp of the neural mechanisms at work and hope the new findings and future research will lead to new therapeutic and pharmacological approaches to treating a variety of emotional disorders.”
Research psychiatrist Dr. Laurie Litchi of Santa Fe, N.M., was skeptical of transferring any knowledge gained in the experiment to patients with mental problems. “There is a huge difference in the brains of people who have been traumatized. I don’t think the researcher can assume the same mechanisms will be functioning in the same way in traumatized populations,” Litchi said.
