Researchers Identify How We Store Information in Our Memory

Photo by Milad Fakurian on Unsplash

Our memories are rich in detail. We vividly remember things like the color of our house, the layout of our kitchen, and the front of our favorite cafe. How the brain encodes this information has  puzzled neuroscientists for years.

In a new study conducted at Dartmouth College, researchers have identified the neural coding mechanisms that enable the transfer of information between sensory and  memory areas of the brain. The results will be published in Nature Neuroscience.

Prior to this study, the classical understanding of brain organization was that the brain's perceptual regions represented the world "as it is," and that the brain's visual cortex "represented" the outside world based on how light hit the retina. It was expressed locally on the retina. In contrast,  the brain's memory areas were thought to represent information in an abstract form, without details about its physical properties. However,  the co-authors say this explanation does not take into account that  these regions may actually share a common code in the brain when encoding and retrieving information. That's what it means.
 
"We found that memory-related brain areas encode the world like a `photographic negative' in space," says co-lead author Adam Steel, a postdoctoral researcher in the Department of Psychological and Brain Sciences and fellow in the Neukom Institute for Computational Science at Dartmouth. "And that 'negative' is part of the mechanics that move information in and out of memory, and between perceptual and memory systems."

A series of experiments tested participants' cognition and memory while recording their brain activity  using  functional magnetic resonance imaging (fMRI). The research team identified a contralateral push-pull-like coding mechanism that regulates interactions between sensory and memory areas in the brain.
 
The results showed that when light hits the retina, the brain's visual cortex responds by increasing its activity and representing patterns in the  light. Memory areas of the brain also respond to visual stimuli, but unlike visual areas,  neural activity decreases when  the same visual pattern is processed.
 
The co-authors report  three unusual findings in this study. The first is the discovery that  visual coding principles are stored in memory systems.
 
The second reason is that this visual code is upside down in the memory system. "When you see something in your visual field, neurons in the visual cortex are activated, but neurons in the memory system are turned off," said lead author Caroline Robertson, assistant professor of psychology and brain science at Dartmouth College.
 
Third, this relationship is reversed during memory retrieval. "When you close your eyes and remember that the visual stimuli are in the same room, the relationship is reversed, meaning your memory system drives and inhibits neurons in the sensory area," Robertson said.

"Our findings provide a clear example of how shared visual information is used by memory systems to focus or defocus retrieved memories." Co-author Ed Shilson, Lecturer in Human Cognitive Neuroscience at the University of Edinburgh, said.

The research team will now investigate how this push-pull dynamic between perception and memory contributes to challenges in clinical diseases, including Alzheimer's disease.