Suppressing Negative Emotional Memories

September 2007 Research from the Center for Neuroscience and the Institute of Cognitive Sciences at the University of Colorado at Boulder published in Science has shown that negative emotional memories can be suppressed with practice, offering the possibility of new treatments for people suffering from a range of conditions including post-traumatic stress disorder, phobias, depression, anxiety and obsessive-compulsive syndrome.

The study by lead author and doctoral candidate Brendan Depue, together with associate professor Tim Curran and professor Marie Banich measured brain activity in subjects trained to suppress memories of negative images and identified two neural mechanisms operating in the prefrontal region of the brain.

Brendan 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. 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."

Subjects were asked to memorize 40 different pairs of pictures, each consisting of a "neutral" human face and a disturbing image (e.g. a car crash, a wounded soldier, a violent crime scene, an electric chair). Subjects were placed in MRI scanners and shown only the face image from each pair. They were asked to either think about, or not think about, the disturbing image previously associated with it.

Researchers found that the resulting functional brain imaging scans indicated that coordination for memory suppression occurred in the prefrontal cortex with two specific regions, the hippocampus and amygdala appearing to work together to suppress particular posterior brain regions like the visual cortex, involved in visual recall, memory encoding and retrieval, and emotional output.

Researchers commented:

"These results indicate memory suppression does occur, and, at least in non-psychiatric populations, is under the control of prefrontal regions."

Bernard Depue explained that the most anterior portion of the prefrontal cortex is a relatively recent human evolutionary feature and is greatly enlarged compared to great apes. Study participants were able to "exert some control over their emotional memories. By essentially shutting down specific portions of the brain, they were able to stop the retrieval process of particular memories."

The researcher speculated that "memory suppression could be a positive evolutionary trait" suggesting that a Stone Age hunter would have starved if unable to deal with traumatic memories of a close encounter with a lion while hunting for food.

Bernard Depue continued:

"It is not clear to what extent an extremely traumatic emotional memory, like a violent battlefield incident or a crippling car accident, manifests itself in the human brain. In cases like this, a person could need thousands of repetitions of training to suppress such memories. We just don't know yet."

Bernard Depue concluded:

"The concept of repressed memories originated by psychologist Sigmund Freud more than a century ago, is extremely controversial. There is considerable debate today over whether repressed memories and suppressed memories are interchangeable terms, and even as to whether repressed memories exist at all."

"The debate over repressed memories probably won't be resolved in my lifetime. I think the important thing here is that we have identified neural mechanisms with potential for helping the clinical community develop new therapeutic and pharmaceutical approaches for people suffering from emotional disorders."

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