Human brain works backwards to retrieve memories

Representational Image

A new study, conducted at the University of Birmingham now says that when we remember a past event, the human brain reconstructs that experience in reverse order.

The study adds that understanding how the brain retrieves information could help better assess the reliability of eye witness accounts.

The study, published in Nature Communications, was carried out by researchers in the Centre for Human Brain Health. They reconstructed the memory retrieval process, using brain decoding techniques that make it possible to track when in time, a unique memory is being reactivated in the brain.

Researchers found that, when retrieving information about a visual object, the brain focuses first on the core meaning and only afterwards recalls more specific details.

Notably, this is in sharp contrast to how the brain processes images when it first encounters them.

Speaking about it, lead author of the study, Juan Linde Domingo said, "We know that our memories are not exact replicas of the things we originally experienced."

He further added, "Memory is a reconstructive process, biased by personal knowledge and world views - sometimes we even remember events that never actually happened. But exactly how memories are reconstructed in the brain, step by step, is currently not well understood."

The study saw participants view images of specific objects and then learned to associate each image with a unique reminder word. They were later presented with the reminder word and asked to reconstruct the associated image in as much detail as possible.

Brain activity was recorded throughout the task via 128 electrodes attached to the scalp, allowing the researchers to observe changes in brain patterns with millisecond precision. Finally the researchers trained a computer algorithm to decode what kind of image the participant was retrieving at different points in the task.

Maria Wimber, senior author of the study inferred, "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."

She added that 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.

Domingo added that if memories prioritise conceptual information, it also has consequences for how they change when we repeatedly retrieve them.

"It suggests they will become more abstract and gist-like with each retrieval. Although our memories seem to appear in our 'internal eye' as vivid images, they are not simple snapshots from the past, but reconstructed and biased representations," Domingo added.

The team is currently also looking in more detail at how and where the brain reconstructs more complex memories. Once the pathway of memory retrieval is established in the healthy brain, researchers can also start looking into how it is altered in healthy ageing, or how this pathway might contribute to the over-generalization of memories in conditions like post-traumatic stress disorder.