Researchers solve mystery of how our brains retrieve memories

14 Jan 2019

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A team in the UK has sifted through the human mind to discover how we retrieve memories, revealing that we trace back our steps.

Have you ever wondered how you remember what you remember? What makes you remember one particular incident 10 years ago that may have had little effect on your life in the long term?

To help solve this mystery, a team of researchers from the University of Birmingham has studied the human mind in great detail to reveal that the brain reconstructs a particular experience, much like how Hansel and Gretel left a trail of breadcrumbs to find their way home.

In a paper published to Nature Communications, the researchers described how they found that the brain remembers a past event in reverse order. For example, when trying to remember something about a particular object, the brain focuses first on its core meaning, following up afterwards in more specific detail.

This sharply contrasts with how the brain typically processes images when it firsts encounters them. When we see a complex object for the first time, we first perceive its patterns and colours, while meaningful information about it – telling us what it is – comes later.

“Memory is a reconstructive process, biased by personal knowledge and world views. Sometimes, we even remember events that never actually happened,” said Juan Linde Domingo, lead author of the study. “But exactly how memories are reconstructed in the brain, step by step, is currently not well understood.”

Is it hardwired?

Using brain decoding techniques that make it possible to track when in time a unique memory is being reactivated in the brain, the team asked study participants to look at images of specific objects. They were later presented with the reminder word and asked to reconstruct the image in as much detail as possible.

By recording brain activity through 128 electrodes attached to each person’s scalp, the researchers could see changes in brain patterns with millisecond precision. A computer algorithm was then trained to decode what kind of image the participant was retrieving in the task.

Senior author of the study, Maria Wimber, said: “We were able to show that the participants were retrieving higher-level, abstract information, such as whether they were thinking of an animal or an inanimate object, shortly after they heard the reminder word. It was only later that they retrieved the specific details – for example, whether they had been looking at a colour object, or a black-and-white outline.”

This, the researchers added, suggests memories will become more abstract and gist-like with each retrieval. While they seem to appear in our ‘internal eye’ as vivid images, they are actually reconstructed, biased representations.

Whether this reversed reconstruction cascade is ‘hardwired’ in the brain will be analysed in follow-up studies. It could be shown if the sequence of reconstruction remains stable under different conditions – for example, when a person consciously focuses their attention on specific details during learning.

Colm Gorey was a senior journalist with Silicon Republic