The Fading of Negative Experiences: Active Suppression Weakens Unwanted Memories

Summary: Actively forgetting a negative experience may help to prevent bad memories from constantly intruding on a person’s awareness and halt rumination.

Source: Max Planck Institute

Many people have had negative experiences in their lives that they would prefer not to remember. However, there are sometimes moments when the events come back to life.

Often, such unwanted memories are triggered by harmless objects that were also present during the original experience: The rubber boot that reminds us of the flood; the shoe for the car accident; the teddy bear of the injured child.

However, earlier studies had found that if a person actively pushes the emerging images out of their consciousness, the associated scenes become more difficult to remember afterwards. They are forgotten.

Until now, however, it was unclear what happens to the stored scenes—did they actually fade away? And how can this forgetting be observed in the brain?

“If you actively suppress a memory and then try to recall it again, the images appear less vividly than before,” Ann-Kristin Meyer, a doctoral student at MPI CBS, explains the results of the study, now published in the journal eLife. According to the study, the participants saw the images less clearly in their inner eye. Sometimes they even disappeared completely.

“We also observed that this fading of a memory is accompanied by a lower reactivation of the memory trace in the brain.”

That is, the specific brain activity that had occurred during the original experience changed, making it more difficult to recall the images.

Moreover, the memory traces seemed to become particularly weakened in those people, who were particularly good at suppressing the memories.

From earlier studies, the scientists already knew what happens in the brain during suppression. The prefrontal cortex, a brain structure behind the forehead, inhibits the activity of the hippocampus. The hippocampus is a structure in deeper brain regions that ensures that a memory trace gets reactivated. The current results suggest that this inhibition leads to a persistent and long-term weakening of the memory trace.

“Forgetting has a largely bad reputation,” says Roland Benoit, study leader and head of the Adaptive Memory Research Group at MPI CBS.

“However, active forgetting may be a helpful mechanism to prevent memories of bad experiences from constantly intruding into our awareness.” By controlling our thoughts, we can weaken our memories and possibly erase their neural traces in the brain, he said.

It is not yet clear why some people are better at actively forgetting than others. However, it is particularly difficult for those with depression or post-traumatic stress disorder. Future studies should now determine whether, and how, deliberate forgetting contributes to mental health.

The scientists investigated such forgetting in a three-step procedure. In a first step, the participants learned to associate pictures of negative experiences with a neutral object, such as a flood disaster with a rubber boot, a car accident with a lost shoe, and an injured person with a teddy bear. Specifically, they saw the scenes with the respective objects several times.

This shows a sad woman sitting at a window
From earlier studies, the scientists already knew what happens in the brain during suppression. Image is in the public domain

Eventually, the boot, shoe, and teddy bear began to automatically evoke the bad images. The scientists then measured brain activity using magnetic resonance imaging (MRI), while the participants recalled the scenes with the help of the objects.

In a second step, the people were only shown the objects. In some cases, they were asked to recall the scene. In other cases, they were asked to suppress any thoughts of the scene. In the last step, they were again shown all the objects, one after the other, and tried to remember each respective scene. This allowed the research team to check whether the avoided memories had actually faded.

Critically, it also enabled them to compare the pattern of brain activity before and after suppression.

In another series of measurements, the researchers had recorded the typical pattern of activity that occurs in the brain during the experience of distressing images. They used this typical pattern as a template to gauge the reactivation of the individual memories.

About this PTSD research news

Author: Press Office
Source: Max Planck Institute
Contact: Press Office – Max Planck Institute
Image: The image is in the public domain

Original Research: Open access.
Suppression weakens unwanted memories via a sustained reduction of neural reactivation” by Ann-Kristin Meyer et al. eLife


Abstract

Suppression weakens unwanted memories via a sustained reduction of neural reactivation

Aversive events sometimes turn into intrusive memories. However, prior evidence indicates that such memories can be controlled via a mechanism of retrieval suppression.

Here, we test the hypothesis that suppression exerts a sustained influence on memories by deteriorating their neural representations.

This deterioration, in turn, would hinder their subsequent reactivation and thus impoverish the vividness with which they can be recalled. In an fMRI study, participants repeatedly suppressed memories of aversive scenes. As predicted, this process rendered the memories less vivid.

Using a pattern classifier, we observed that suppression diminished the neural reactivation of scene information both globally across the brain and locally in the parahippocampal cortices. Moreover, the decline in vividness was associated with reduced reinstatement of unique memory representations in right parahippocampal cortex.

These results support the hypothesis that suppression weakens memories by causing a sustained reduction in the potential to reactivate their neural representations.

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  1. Anyone who works with people knows that suppression is only shoving things into the scary box that “we don’t look at”. Instead of just measuring the conscious recall or recognition of a scene, why don’t you measure all of the corresponding symptoms that will go along with “active suppression”, such as memories that then increase during stressfull moments, dreams, intoxication, lack of support…… Then also measure the anxiety, ocd, and other symptoms that are a result of the energy that it takes to keep trying to forget ones life. Even if this technique does work, the effect is essentially to contract, rather than expand, which means less creativity, less energy for life and more robotic living. The snake just keeps eating its tail. If neuroscience did discover exactly how to “cure” our emotions, the result would be an artless, pointless, existential dystopia in which it wouldn’t matter anymore and people would be suicidal not because of PTSD, but because they no longer cared about living. I will agree that some people would trade their trauma and rumination easily, for a more mundane life (just visit an AA meeting), but why do that when there are ways to actually resolve human dramas. Resolution and freedom from past memories is actual healing. But, it’s not just a memory. These memories are part of a theme, such as what one thinks about oneself, how they see the world, what there philosophy or meaning of life is about. Just a couple of examples of resolving unwanted memories would be: mindfulness and acceptance using a bhuddist perspective, psychodynamic work to understand past experience, intentional action to help others to recognize the unity of humans, time in nature, the intentional use of psychedelics, exposure therapies galore. Do you really think that neuroscience will solve Shakespearean dilemmas or answer the anything meaningful for humans?

  2. I’ve done this for years. Though being married and havin my wife ask questions about my past has caused issues because I truly don’t remember.

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