Understand why some memories come back (and others don’t)

As a child, in the early 1980s, I fell in love with My Little Pony, the colorful plastic horse figures with long manes. I also had the brand’s Show Stable, which was parked in our TV room and filled with my beloved ponies. But as I progressed through elementary school, I ended up tidying up my stable and forgot about the toys I once loved.

At the end of 2003, I hadn’t thought about my ponies for over 15 years. Then VH1 aired a nostalgic 1980s show in which celebrities remembered bygone pop culture. One actress held up a My Little Pony figure (a Twinkle-Eyed variety) and noted, “It’s enough to mesmerize any child. I mean, shiny diamond eyes? ”

I had this spellbinding toy, I suddenly realized. The memories came back to me, and I wondered where they had been all those years.

Lucky for me, scientists continue to learn where our long-term memories go when not in use. For people who don’t suffer from memory loss or other neurological disorders, sleepers aren’t necessarily forgotten. But they do require the correct recovery index to be recalled.

The basics of memory storage

Scientists have a classification system for different types of memories: two broad categories known as explicit and implicit memories. Within explicit memories are episodic memories, in which we remember events, as well as semantic memories, which contain our general knowledge of the world. Meanwhile, implicit memories are the subconscious procedures we use in our daily lives, such as remembering how to type on a keyboard or reheat lunch in the microwave.

The brain’s two hippocampi are responsible for processing short-term memories and transferring information to other parts of the brain for long-term storage. But scientists are still studying how the hippocampus selects specific information for storage.

“Memories that are more emotionally meaningful or important to survival tend to stick with us. Those that aren’t tend to fade,” says Borna Bonakdarpour, behavioral neurologist at Northwestern Medicine in Chicago.

My Little Pony’s Twinkle-Eyed variety wasn’t important to my survival, but Bonakdarpour says she must have been emotionally meaningful and played with regularly. This is because repeated exposure is important.

“If you see an object and interact with it multiple times, it tends to stay in the brain longer,” he says. “If you see it once, the memory might fade.” The brain is very efficient. “

In fact, scientists are learning that forgetting information is not the result of functional failure, but actually serves to improve mental function: lost memories are part of an intentional mechanism that may be intended to help us deal with future events without confusing us too much. details. For example, remembering every detail of a traumatic event, such as a dog attack, can make generalization and preparation for future harm more difficult.

Recovery indices

As memories are formed, the seahorses sort the information based on the five senses and send it to the prefrontal areas for storage. “When new information gets to our brains to memorize, it’s the librarians. They sort the information on a specific shelf, ”says Kei M. Igarashi, assistant professor of anatomy and neurobiology at the University of California, Irvine.

It’s even possible that a person’s thoughts trigger a memory. “Sometimes thoughts bring back concepts and experiences from the past. It is not an external stimulus, it is internal. This is how we solve problems as humans – you have a memory of how things worked. “

In some cases, we recall a memory when one of the five senses is stimulated. Igarashi says seeing the Twinkle-Eyed Pony was the visual stimulus needed to awaken memory for the first time in over a decade. “It went from the visual cortex to the hippocampus, and the hippocampus said, ‘Hey, we had that information,’ and got it,” he says.

Igarashi’s research focuses on memories associated with smells, and he says researchers believe there is an evolutionary component to remembering the danger associated with smells. “The smell of smoke is the most triggering,” said Igarashi. “It’s very sensitive for us. We know if there is a fire we need to avoid. We don’t want to test it.

We can also feel positive associations with certain smells, says Igarashi, because dopamine helps in memory formation. His research has identified how the fan-shaped cells, which are found in the lateral entorhinal cortex of the medial temporal lobe and controlled by dopamine, are responsible for receiving new associative memories.

The discovery of dopamine emerged from experiments in which Igarashi’s team used electrophysiological recordings and optogenetic to determine the activity of mouse ventilator cells as they learn to associate rewards with specific smells.

Positive associations

Research on memory associations also helps explain why we connect the scent of chlorine with a summer swim or pine needle puffs with Christmas. More specifically, it could play a role in neurodegenerative diseases: Igarashi’s team is studying associated memories in order to better understand Alzheimer’s disease. His team found that Alzheimer’s patients lose their spatial awareness – and sense of where they are – due to a disruption in the hippocampus caused by deficiency to the entorhinal cortex. He hopes to learn how scientists can stop this progression before it causes significant damage.

As scientists research memory in hopes of alleviating symptoms of Alzheimer’s disease, they’ve also learned more about memory in patients. Bonakdarpour says people with Alzheimer’s and dementia lose their short-term memory and eventually forget their age. “At some point, they start living into their teenage years and they appreciate things in their teenage years,” he says.

Researchers have learned that sound is the last of the five senses lost by a person with memory impairment. Playing music from a patient’s younger years can be enjoyable, but Bonakdarpour says clinicians need to be careful if the music has a negative association. A patient, for example, who survived the Holocaust in Europe could be triggered in traumatic memories upon hearing a track that sounds like a German walking song.

The clinic therefore relies on questionnaires to learn more about the patient’s past and preferences so that they can play music that brings back positive memories.

“That’s what we did last year during lockdown,” he says. “Our patients were stuck in the hospital and they couldn’t see the visitors. We played music for them that we knew they liked. We found it calming. They loved it. ”

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