Researchers identify new coding mechanism that transfers information from perception to memory

Our memories are rich in details: we can vividly recall the color of our house, the layout of our kitchen or the front of our favorite café. The way in which the brain encodes this information has long intrigued neuroscientists.

In a new Dartmouth-led study, researchers have identified a neural coding mechanism that allows information to be transferred between perceptual regions and memory areas of the brain. The results are published in Natural neuroscience.

Before this work, the classic understanding of brain organization was that the brain’s perceptual regions represented the world “as it is”, with the brain’s visual cortex representing the outside world based on how light falls on it. the retina, “retinotopically”. In contrast, memory areas of the brain were thought to represent information in an abstract format, lacking details about its physical nature. However, according to the co-authors, this explanation ignores the fact that as information is encoded or recalled, these regions may actually share a common code in the brain.

“We found that brain areas related to memory encode the world as a ‘photographic negative’ in space,” says co-lead author Adam Steel, a postdoctoral researcher in the Department of Psychological and Brain Sciences and a research fellow at the Neukom Institute for Computer Sciences. at Dartmouth. “And this ‘negative’ is part of the mechanisms that move information in and out of memory, and between perception and memory systems.”

In a series of experiments, participants were tested on their perception and memory while their brain activity was recorded using a functional magnetic resonance imaging (fMRI) scanner. The team identified an opposite push-pull coding mechanism, which governs the interaction between the perception and memory areas of the brain.

The results showed that when light hits the retina, visual areas of the brain respond by increasing their activity to represent the light pattern. Memory areas of the brain also respond to visual stimulation, but unlike visual areas, their neural activity decreases when processing the same visual pattern.

The co-authors report that the study presents three unusual findings. The first is their discovery that a visual coding principle is preserved in memory systems.

The second is that this visual code is reversed in memory systems. “When you see something in your visual field, neurons in the visual cortex are firing while those in the memory system are quiet,” says lead author Caroline Robertson, assistant professor of psychology and brain sciences at Dartmouth. .

Third, this relationship reverses during memory recall. “If you close your eyes and remember these visual stimuli in the same space, you will reverse the relationship: your memory system will work, suppressing the neurons in the perceptual regions,” says Robertson.

“Our results provide a clear example of how shared visual information is used by memory systems to highlight and blur recalled memories,” says co-senior author Ed Silson, senior lecturer in human cognitive neuroscience at the University of Edinburgh.

In the future, the team plans to explore how this push and pull dynamic between perception and memory may contribute to challenges faced in clinical conditions, including in Alzheimer’s disease.