Mental & Emotional Health

Suppressing Unwanted Memories

Researchers at the University of Cambridge and the  Medical Research Council Cognition and Brain Sciences Unit in the UK have shown that suppressing unwanted memories reduces their unconscious influences on subsequent behavior. The team has also shed light on how this process happens in the brain.

A release from Cambridge explains that the study, published online in March 2014 in Proceedings of the National Academy of Sciences challenges the idea that suppressed memories remain fully preserved in the brain's unconscious, allowing them to be inadvertently expressed in someone's behavior. The results of the current research suggest instead that the act of suppressing intrusive memories helps to disrupt traces of the memories in the parts of the brain responsible for sensory processing.

The investigators examined how suppression affects a memory's unconscious influences in an experiment that focused on suppression of visual memories because intrusive unwanted memories are often visual.

After a trauma, most people report intrusive memories or images and people will often try to push these intrusions from their mind as a way to cope. The frequency of intrusive memories decreases over time for most people. It is critical to understand how the healthy brain reduces these intrusions and prevents unwanted images from entering consciousness so that researchers can better understand how these mechanisms may go awry in conditions such as post-traumatic stress disorder.

Participants were asked to learn a set of word-picture pairs so that, when presented with the word as a reminder, an image of the object would spring to mind. After learning these pairs, brain activity was recorded using functional magnetic resonance imaging (fMRI) while participants either thought of the object image when given its reminder word, or instead tried to stop the memory of the picture from entering their mind.

The researchers studied whether suppressing visual memories had altered people's ability to see the content of those memories when they re-encountered it again in their visual worlds. Without asking participants to consciously remember, they simply asked people to identify very briefly displayed objects that were made difficult to see by visual distortion. In general, under these conditions, people are better at identifying objects they have seen recently, even if they do not remember seeing the object before—an unconscious influence of memory. Strikingly, they found that suppressing visual memories made it harder for people to see the suppressed object laer compared to other recently seen objects.