Why forgetting is actually a crucial part of memory

Ever feel like your brain is so full of information, you need to toss something out in order to learn something new?

That might be more true than you think.

Remembering something important makes our brains discard any similar memories that might compete for its attention, according to a new study published Monday. And actively recalling some of these memories while ignoring others can cause those overlooked memories to fade.

Similar memories compete with one another

Similar memories — like one of you dropping your keys on the kitchen table and another of you putting those keys on your desk — get stored in the same cabinet. Each time you shuffle through one of those cabinets of snapshots to pick one out, it causes the other snapshots to fade a bit.

If you keep pulling out the same photograph over and over (or recalling the memory of your keys in the same place), your brain marks it as important, and the other images get more and more faint. Eventually, only the important memory remains distinguishable from the rest.

Researchers have been testing the idea that the brain intentionally wipes away similar memories in favour of preserving the ones it labels “important” for years, but only this most recent study has gotten close to narrowing down precisely how it happens.

How our brain decides which memories to keep

To find out what’s going on in the brain when we remember certain things and forget others, the scientists had volunteers memorize that a specific word was linked with two different, unrelated pictures.

To remember that the word “sand” was linked with an image of Marilyn Monroe, for example, someone might picture Marilyn on a sandy beach. Then, to remember that “sand” was also linked with a hat, someone might think of the hat covered in sand.

Every time the volunteers linked a specific image with a word, they formed a distinct pattern in the area of the brain responsible for storing visual information. The researchers came up with a way to identify each of these patterns (let’s call them the “Marilyn pattern,” for example, and the “hat pattern”) on a computer.

After the volunteers had linked both images with the word, the researchers told them they only had to worry about remembering the first one.

Next, they took the volunteers to another room, where the word “sand” was being flashed occasionally on a blank screen. At first, the volunteers’ brains displayed both the Marilyn pattern and the hat pattern when they saw the word. But over time, the hat pattern grew dim while the Marilyn pattern stayed clear.

In other words, the volunteers were remembering the image of Marilyn by discarding the image of the hat.

“It’s the brain’s way of keeping everything that’s up to date, and telling the rest it can go,” University of Birmingham psychology professor and the study’s lead author Maria Wimber told Business Insider.

We forget in order to remember

While it sounds inconvenient (who wants to forget where they last stashed their keys?), there might be a very important reason that we forget similar memories.

Take for example the last time you got a new bank account, suggests Wimber. When you walk up to the ATM, you automatically find yourself typing in the PIN number linked with your old account. But the more you visit the ATM and get used to recalling the new PIN number, the more the old number fades in your memory — and the more easily you recall the new one.

Apply this knowledge to your keys by storing them in the same location every time (reducing your brain’s supply of competing similar memories), and you’ll be less likely to forget where you put them last.

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