Through movies and other forms of popular culture, everybody knows that suppressing memories of tragedies is bad for your mental health. Completely unbeknownst to you, those tragic images that are buried deep inside your unconscious can fester for years -- decades even -- affecting everything from your behavior to your innermost thoughts.

Or maybe not. New research published in PNAS suggests that this commonly held belief from pop psychology may not actually be true.

The authors had 24 participants go through a three-stage experiment. (See first figure.)

In the first stage ("learning"), volunteers learned to associate words with pictures. For instance, the word "duty" was associated with a picture of binoculars. In the second stage ("TNT," meaning "think/no-think"), participants were shown the cue word and told to either think about the associated object or to not think about the associated object. In the third stage, blurry images of the objects they studied or brand new objects were displayed. When the object became recognizable, the participants were told to press a button. Stages #2 and #3 were performed inside of an fMRI machine in order to determine which parts of the brain were active.

The researchers made two very interesting discoveries. The first was that volunteers took longer to recognize objects that they were told to not think about. (See second figure.)

As shown, it took volunteers 2,482 milliseconds (ms) to recognize objects they hadn't seen before ("unprimed"). Objects that the volunteers learned but did not use in Stage #2 of the experiment served as a "baseline" control. It took them 2,249 ms to recognize these objects, and 2,269 ms to recognize objects that they actively thought about. However, the volunteers took 2,310 ms to identify the objects they were told specifically not to think about. This implies that suppressing visual memories of an object affects a person's ability to later perceive the very same object.

The fMRI data the researchers collected led them to a second discovery. Suppressing images activated the right middle frontal gyrus (MFG). The authors used Bayesian modeling to conclude that the right MFG was suppressing the brain region involved in visual perception, called the fusiform cortex. They believe this explains why it took longer for volunteers to recognize objects that they had actively suppressed in their minds.

Of course, this research does not disprove the existence or effect of unconscious memories. But, it certainly challenges the notion that suppressing memories is bad. On the contrary, suppressing traumatic images may make it harder to recall or experience them again in the future.

So go ahead and suppress all those horrible childhood memories you have of being bullied on the playground or accidentally walking in on your parents. It might just work.

Source: Pierre Gagnepain, Richard N. Henson, and Michael C. Anderson. "Suppressing unwanted memories reduces their unconscious influence via targeted cortical inhibition." PNAS. Published online before print: 17-Mar-2014. doi: 10.1073/pnas.1311468111