When you process your day-to-day experiences and turn them into memories your brain could easily get overwhelmed by the sheer volume of incoming data. To counter this, your brain is wired to identify and forget distracting, irrelevant memories that could compete with more important ones. This lets you prioritize goal-oriented, hazard-avoiding memories, so you can best adapt to your environment by finding food and mates and dodging an untimely death. The process is called selective amnesia, a sort of Darwinian natural selection of memories that help with survival.
A team at the University of Cambridge is building on their previous findings that recalling memories from your past causes you to forget competing memories. Their new study out today in Nature Communications, in collaboration with researchers from The Favaloro University in Argentina, shows that trying to recall a memory doesn’t simply allow the brain to passively let go and forget competing memories. Recall of one memory seems to actively snuff out the competition. The handy work of the memory hitman in our brains is referred to as active forgetting or retrieval-induced forgetting.
How it works
Reaching back for a specific memory triggers an inhibitory mechanism that suppresses competing memories. The inhibitory mechanism is a signal, a directive coming from the prefrontal cortex. The prefrontal cortex already performs this function with behavior. It tamps down on automatic, habitual responses that may distract from new and more adaptive responses. From the paper: “If the prefrontal cortex suppresses competing responses, it may also suppress competing memories, initiating a signal that triggers active forgetting.”
From the dangerous to the therapeutic
The findings raise many possible benefits and handicaps when negotiating our own thoughts and memories, and those of others. Craig Brierley, head of research communications at Cambridge warns “if the police interview a witness to a crime, for example, their repeated questioning about selected details might lead the witness to forget information that could later prove important.”
From a more positive therapeutic perspective, it seems like it might be possible to flip the active forgetting process . If you’re ruminating over (actively recalling) a troubling memory, it might be possible to actively recall another competing but less relevant memory associated with the troubling one.
“Quite simply, the very act of remembering is a major reason why we forget, shaping our memory according to how it is used,” says the paper’s lead author, Michael Anderson via press release. “People are used to thinking of forgetting as something passive. Our research reveals that people are more engaged than they realize in actively shaping what they remember of their lives. The idea that the very act of remembering can cause forgetting is surprising and could tell us more about people’s capacity for selective amnesia.”
Selective amnesia has been demonstrated across a number of species. For this rodent study, the researches tested 63 rats individually. Rats are curious by nature and will investigate any new object in their environment.
Each rat was allowed to roam around freely inside a test area and explore an object (object A) for five minutes. The rat was then removed from the area. 20 minutes later the rat was returned to the test area only to find a new object (object B) which it was allowed to explore for another five minutes.
Then began the retrieval practice phase where the scientists repeatedly put the rat back in the test area with object A as well as some cool new object. The rat quickly tired of object A. Like us, rats want the next shiny new thing. The rat’s clear preference for the new object confirmed for the researchers that the rat remembered object A because it was no longer curious about it.
The researchers wanted to see how repeated exposure and recall of object A impacted recall for object B. In the final phase of the experiment conducted a half hour later, the rat was put back in the test area with object B and a brand new object. The rat investigated both object B and the new object with the same degree of curiosity. This demonstrated that repeated recall of object A caused the rat to forget object B.
For the control, the researchers skipped the retrieval practice phase and let the animal relax for the same amount of time. The control rats demonstrated excellent recall of object B.
The team then zeroed in on the rats’ medial prefrontal cortex, an area in rat brains parallel to an area in human brains that allows us to actively forget. Using the drug, muscimol, to temporarily dampen the signals from this region, they found the rats were no longer able to forget competing memories, pointing to the source of the signal for actively forgetting memories.
“This discovery suggests that this ability to actively forget less useful memories may have evolved far back on the ‘Tree of Life’, perhaps as far back as our common ancestor with rodents some 100 million years ago,” says Anderson via Eurekalert.
The team is furthering their research to get a better understanding of how this process works on a cellular, and possibly, a molecular level and how it could possibly treat post-traumatic stress disorder (PTSD).