Have you ever clearly remembered a trivial detail, like a squirrel seen from afar, while you’ve already forgotten what you ate yesterday? You’re not strange: it’s your brain that chooses what to keep and what to let go. New research explains why.
During a car trip in New Hampshire, Chenyang “Leo” Lin, a young neuroscientist at Boston University, noticed some squirrels in the trees. An ordinary scene, yet he remembered it clearly. That detail struck him so much that it inspired a study on the functioning of memory, today published in the journal Science Advances. The brain does not record everything, but it “protects” certain memories more than others, especially if they are close to emotional experiences. But emotion is not enough: a conceptual connection between events is also needed.
We don’t remember everything
Lin grew up in a city in southern China, where squirrels and woods were not part of the landscape. That unusual detail stuck, and not by chance. According to him and Professor Robert Reinhart, who coordinated the study, emotions can strengthen even neutral memories, but only if these have something in common with the emotional event.
Have you ever received important news? Do you remember what music was playing in the background or where you were? Probably yes. This happens because emotions work like “memory glue”, and can make more stable even what, on its own, would not have remained imprinted.
To better understand the mechanism, the researchers conducted ten experiments involving 648 people. Each participant saw a series of images – some of animals, others of objects – followed by a small reward (money) or a mild electric shock. The next day, without warning, they were asked what they remembered.
The result? The emotional moments strengthened the memories of what happened immediately afterwards, but also – and only in certain cases – what happened shortly before. The brain seems to work with what scientists call selective logic retroactive memory enhancement.
But there’s one key detail: for a neutral memory to be saved, it must resemble the emotional one, either in form or category. In practice, seeing a bison could also fix the memory of a rabbit just glimpsed, but not that of a screwdriver or a cup.
Fragile memories need help the most
This discovery is linked to a theory called behavioral tagging: When we have a weak but significant experience, the brain assigns it a temporary “bookmark”. If something emotionally strong happens shortly afterwards – whether positive or negative – and the two events are conceptually similar, the brain uses that energy to make even the most fragile memory more solid.
But be careful: not all memories work the same way. In the study, images of animals – harder to remember, but more emotionally engaging – were the ones that benefited most from this “rescue effect”. The images of tools, on the other hand, were easier to remember on their own, without the need for emotions.
This means that the brain chooses intelligently: it reinforces what it would risk losing, if it deems it relevant. A mechanism that, from an evolutionary point of view, makes sense: remembering the route you took to escape from a danger, or the animal that scared you, can make the difference between surviving or not.
Practical applications: education, memory and trauma management
These discoveries could also have concrete effects in everyday life. At school, for example, connecting difficult notions to emotionally engaging content – a story, an experience, a game – could help students remember better.
Even when caring for people with dementia, using meaningful images or sounds could make important memories from everyday life more stable. Likewise, in a clinical setting, this mechanism could be used to “deactivate” traumatic memories, preventing the brain from involuntarily reinforcing them.
Of course, there are limits. The experiments took place in the laboratory, with simple images and controlled situations. Memory in real life is more complex. The researchers now hope to use tools such as MRI to observe what happens in the brain as these mechanisms activate.
One last interesting note: To measure how similar the memories were to each other, the researchers also used artificial intelligence. A neural network analyzed the images to understand how much visual and conceptual similarity there was between the stimuli. The more similar two images were, the stronger the memory effect.
In practice, we don’t remember everything, but we remember better what resembles something emotionally relevant. Our brain leaves nothing to chance.
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