US researchers have identified the parts of the brain that are involved with suppressing unpleasant memories, a finding that could have implications for treating depression or post traumatic stress disorder, according to a study released Thursday.
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.
The scans showed that two specific regions of the prefrontal cortex -- what neuroscientists call the seat of cognitive control -- appear to work in tandem to modulate posterior brain regions like the visual cortex, the hippocampus and amygdala. These areas are involved in tasks such as visual recall, memory encoding and retrieval and emotional expression.
"These results indicate memory suppression does occur, and, at least in nonpsychiatric populations, is under the control of the prefrontal cortex," the investigators reported in the journal Science.
For the purpose of the experiment, the 16 volunteers were given 40 pairs of photographs to study. In each case, an image of a neutral human face was paired with an emotionally disturbing image such as a car crash, a wounded soldier, an electric chair or a violent crime scene.
After memorizing each pair, the volunteers were placed in an MRI (magnetic resonance imaging) scanner. Once inside the machine, they were shown only the neutral face images and instructed to either actively recall the associated image or to actively suppress it.
The results of the scans or fMRIs (functional magnetic resonance imaging) indicated that the volunteers were able to "exert some control over their emotional memories," said Brendan Depue, a doctoral student in neuroscience at the University of Colorado at Boulder, and lead author of the study.
"By essentially shutting down specific portions of the brain, they were able to stop the retrieval process of particular memories," Depue said.
The authors of the paper said they hope that their work will promote further research into better therapies and possibly even drug treatments for people suffering from conditions such as PTSD, phobias, and obsessive-compulsive syndrome. The symptoms of these disorders include flashbacks to disturbing events, and intrusive or obsessive thoughts.
"The first step is to understand how memory suppression works in healthy individuals, and what neural mechanisms are at work," said Depue. "Then you need to look at those same mechanisms in a clinical population and figure out why they aren't functioning properly."