Your memories explained: Why some stick and others don’t

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New research has revealed neurons work together in a specific way to help store memories in one's brain. Source: Getty

Whether it’s the smell of your dad’s aftershave or the taste of your mum’s delicious spaghetti, even the smallest of memories from one’s childhood often remain as clear as ever for years on end. But often when it comes to short-term memory, many hit a wall with difficulty remembering the name of someone they’ve just met or a restaurant they went to the day prior.

It probably seems a little odd that the mind is able to recall things from so long ago and forget things learnt a moment ago, but according to new research there is a reason for it, and no – it doesn’t mean you are suffering from short term memory loss. In fact, according to Caltech researchers, its perfectly normal for people’s minds to be prompted with memories from the past, all due to the the interactions of neurons – nerve cells in the nervous system.

Using mice as test subjects, the scientists developed a test to examine the animal’s activity as they learnt about and remembered a new place. Each mouse was placed in an enclosure which was about five feet long with white walls and symbols marked on different locations such as a bold plus sign and an angled slash.

A treat was then put at either end of the track and researchers sat and waited as the mouse moved around the enclosure searching different areas, all the while measuring the activity of the neurons in part of the animal’s brain where new memories are formed. As it wondered about, the mouse initially couldn’t work out which way to go and sniffed right around before eventually finding the treat.

Single neurons were activated as it started to notice the symbols on the walls and, as the exercise was repeated, more neurons activated as the mouse slowly began to remember where it had been. Essentially, the mouse was recognising where the treat was in relation to each unique symbol.

The next test checked how memories fade over time. This time mice were removed from the enclosure for 20 days allowing time for everything they learnt to disappear. When placed back in after almost three weeks, instead of going through the same process as before to find the treat, the mice were able to remember the task immediately.

While there was different activity by the neurons in this case, scientists were able to discover that the mouse’s memory of the area was clearly identifiable. Put simply, the group of neurons enabled the brain to recall memories even if some of the original neurons fell silent or were damaged.

Although in this case it was mice and their treats, it helps to explain why a certain event in time from 50 odd years ago, like visiting a particular park with friends or always eating a type of ice cream, can still remain so clear in the mind. If someone questions you about your favourite memory as a child, then no doubt at least one thing will pop into your mind – and it’s your neurons that are helping you out.

Putting it into simpler terms, postdoctoral scholar Walter Gonzalez, who led the study published in journal Science, explained it in terms of telling a long and complicated story. He said the neurons are able to work together, like friends recalling an event, to bring a memory to light.

“In order to preserve the story, you could tell it to five of your friends and then occasionally get together with all of them to re-tell the story and help each other fill in any gaps that an individual had forgotten,” Gonzalez said. “Additionally, each time you re-tell the story, you could bring new friends to learn and therefore help preserve it and strengthen the memory. In an analogous way, your own neurons help each other out to encode memories that will persist over time.”

Meanwhile, fellow researcher and professor of biology Carlos Lois explained this new information may be able to help those impacted by memory loss in old age or people affected by diseases such as Alzheimer’s. He said the inability to remember things as you grow older is because a memory is encoded by fewer neurons, meaning as they fail, the memory is lost. But with further research and development of treatments which boost the number of neurons, life could become much easier and joyous for this population.

“For years, people have known that the more you practice an action, the better chance that you will remember it later,” Louis said. “We now thing that this is likely because the more you practice an action, the higher the number of neurons that are encoding the action.

“The conventional theories about memory storage postulate that making a memory more stable requires the strengthening of the connections to an individual neuron. Our results suggest that increasing the number of neurons that encode the same memory enables the memory to persist for longer.”

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What are some of your best memories from your childhood? Do you have difficulty remembering things in the short term?

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