According to a new study published in Nature Communications, when we remember a past event, our brain reconstructs that experience in reverse order: The brain focuses first on the broad details and only afterward recalls the specifics.
Understanding how the brain retrieves information could help us better assess the reliability of eyewitness accounts—especially regarding crimes, after which people often recall the overall gist of an event but recall specific visual details less reliably.
“We know that our memories are not exact replicas of the things we originally experienced,” says lead author Juan Linde Domingo. “Memory is a reconstructive process, biased by personal knowledge and worldviews—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.”
During the study, participants saw images of specific objects and learned to associate each image with a unique reminder word, for example, ‘spin’ or ‘pull.’ The participants 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.
“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,” explains senior author Maria Wimber. “It was only later that they retrieved the specific details, for example, whether they had been looking at a color object or a black and white outline.”
The team is currently 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 aging, or how this pathway might contribute to the over-generalization of memories in conditions like post-traumatic stress disorder.