All of us have at least a few memories we’d like to erase. But deleting them from isn’t always easy. According to a study conducted by researchers at the University of Texas at Austin, forgetting something may require more mental effort than trying to remember it. How did they make this discovery?

Our memories are not static; they are dynamic constructs of the brain that are regularly updated and reorganized according to our life experiences. We are constantly remembering and forgetting information, most often while we sleep. Previous studies have shown that forgetting plays a vital role in preserving memories and eliminating unwanted information. Traditionally, intentional forgetting occurs through passive processes, like withdrawing sustained attention or no longer repeating the memory. This form of forgetting is also associated with the elimination of memory processes during the encoding and recovery phases. When it comes brain research, most studies on the processes involved in intentional forgetting have been focused on brain control structures (like the prefrontal cortex) and long-term memory structures (mostly the hippocampus). The studies aimed to determine whether the brain tried to draw attention away from the bad memory or prevent it from being erased.

The present study opted for an alternative approach focused on the ventral temporal cortex, an area of the brain involved in the processing of sensory and perceptual information (including memories of complex visual stimuli). Jarrod A. Lewis-Peacock, from the Department of Psychology at the Institute of Neuroscience states: “We're looking not at the source of attention in the brain, but the sight of it.” Specifically, the scientists presented adult participants with a series of images (scenes and faces) that they had to either memorize or forget. During the experiment, their brain activity was recorded (using functional magnetic resonance imaging - fMRI).

Analysis of the neuroimaging data provides new evidence that humans have the ability to control what they forget, but that forgetting a stimulus requires more brain activity in the sensory and perceptual areas than remembering it. Indeed, the researchers found that people who were asked to actively forget an image had a higher level of activity in the ventral temporal cortex compared to those who were asked to remember it. Tracy Wang, one of the articles co-authors states that: “A moderate level of brain activity is critical to this forgetting mechanism. Too strong, and it will strengthen the memory; too weak, and you won't modify it. Importantly, it's the intention to forget that increases the activation of the memory, and when this activation hits the 'moderate level' sweet spot, that's when it leads to later forgetting of that experience."

Note that the study participants were able to erase memories of scenes more easily than those of faces. The researchers believe that this is because the latter carry a greater amount of emotional information. According to the authors, this result is also coherent with the nonmonotonic plasticity hypothesis, which predicts that moderately activated memories fade and are forgotten.

In conclusion, this research explores how and why we are able to forget. It opens interesting perspectives on how we may be able to control intentional forgetting; an ability that could be very helpful for people suffering from painful memories.