How Your Brain Deletes Trauma

A new study shows that the act of remembering leads to the subtle forgetting of other memories.

Oivind Hovland/Ikon Images/Corbis

Our brains actually aren’t able to absorb infinite amounts of information: new research has revealed that memories operate on something closer to a one-in, one-out policy.

The process of recall causes people to lose other memories, meaning that our attempts to remember certain things lead to the forgetting of others.

The study—a joint venture between the UK’s University of Birmingham and Cambridge University’s Medical Research Council Cognition and Brain Sciences Unit—is the first of its kind to test our ‘forgetting’ mechanism, monitoring the changes that occur when we try to remember new things. The experiment trained 24 participants to associate words with two unrelated pictures of famous people, scenes and objects.

They were then shown a cue word and asked to recall the image it linked to, reinforcing that particular picture as the dominant memory. For example, if the word ‘sand’ was first associated with a photo of Marilyn Monroe, and secondly, with a hat, participants would press a button indicating that they had recalled Monroe first.

Cue words were repeated at various points throughout the test, which led to the finding that the picture of Monroe continued to be associated with sand more often than the word triggered memories of the hat. The more frequently this choice was made, the more evident it became that reinforcing a specific thought would make it far clearer in the mind.

Conversely, participants' memory of the hat grew weaker, and they became increasingly unable to distinguish which picture they had first been shown when given the choice between two images. The fact that one memory became more vivid while the other grew less clear demonstrated that we have the ability to diminish the power of certain thoughts.

“Remembering can cause forgetting,” explains one of the study’s researchers, Dr. Michael C Anderson, who has worked on a number of suppression theory papers during his career. “It's a form of active forgetting that people aren't necessarily aware of. The patterns of the way we use our memories can shape what remains accessible and what doesn't.”

“Forgetting arises when other competing traces interfere with retrieval and inhibitory control mechanisms are engaged to suppress the distraction they cause,” the paper reads. Dr. Anderson called the results surprising, and said they “could tell us more about selective memory and even self-deception.”

The ability to control what we remember could have enormous implications, ranging from programming trauma victims to eliminate painful memories to strengthening our ability to retain certain types of information. “In the case of truly traumatic experiences, it's necessary to prevent the intrusive memories of those traumas from dominating your day-to-day life,” Dr. Anderson adds. “People who experience persistent reminders, flashbacks and nightmares are very troubled by these things, and it can be debilitating. There is value in reducing the influence of those things on your everyday thoughts.”

The study also notes that this could be an important consideration within the judicial process, as eyewitnesses who are repeatedly quizzed on the same point may consequently lose focus on associated memories, making it appear as though their testimony is not entirely trustworthy.

While the positives of such a technique are rightly pointed out, it is worth reflecting on the downsides that selecting memories could incur. To go back to the paper’s mention of problems arising in court, surely this process could be used to suppress memories of what might have happened in a fateful incident, say, which might lead to witnesses programming themselves to forget vital information. It could also be a gateway to a constant cycle of repression in which nobody ever deals with difficult issues they may have experienced, choosing instead to overpower them without addressing their emotional ramifications.

Being able to actively control our memories may prove useful for some, but burying painful thoughts in a shallow grave is not something that should be encouraged.