Remembering is a reconstructive process, yet little is known about how the reconstruction of a memory unfolds in time in the brain.
In a study published in the journal Nature Communications, a team of scientists from the University of Birmingham and Cardiff University used brain decoding techniques to test the hypothesis that the information flow is reversed when an event is reconstructed from memory.
Across several experiments, the researchers found strong evidence supporting such a reversed stream: they found that, when retrieving information about a visual object, the brain focuses first on the core meaning and only afterwards recalls more specific details; this is in sharp contrast to how the brain processes images when it first encounters them.
“We know that our memories are not exact replicas of the things we originally experienced,” said study lead author Dr. Juan Linde-Domingo, a researcher in the School of Psychology & Centre for Human Brain Health at the University of Birmingham.
“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.”
During the study, participants saw images of specific objects, and then learned to associate each image with a unique reminder word, for example the word ‘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 scientists to observe changes in brain patterns with millisecond precision.
Finally, the team 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,” said study senior author Dr. Maria Wimber, from the University of Birmingham.
“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.”
“If our memories prioritize conceptual information, this also has consequences for how our memories change when we repeatedly retrieve them,” Dr. Linde-Domingo said.
“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.”