Memories are the only paradise from which we cannot be expelled, said the German writer and humorist Johann Paul Friedrich Richter. However, dementias such as Alzheimer’s erase memory and leave the patient in a kind of limbo from which he cannot escape. Understanding how perception and memory work in humans can contribute to better understanding this disease and other pathologies that affect the brain.
Now a team of scientists from Dartmouth University (USA) has used functional magnetic resonance imaging through which they have identified a neural coding mechanism that allows the transfer of information between perceptual regions and memory areas of the brain. The results of their study have been published in Nature Neuroscience.
Our memories integrate a great variety of nuances and details that allow us to remember the colors of the walls and the layout of the furniture in our house, the appearance of a park or beach that we visited, or the place where we have parked the car, but The way the brain encodes this information has always been an enigma for scientists.
Until now, it was considered that the perceptual regions of the brain represented the world “as it is,” and that the visual cortex of the brain represented the external world based on how light hits the retina, “retinotopically.” In contrast, the memory areas of the brain were thought to represent information in an abstract format, which contained no details about its physical nature. However, according to the paper’s co-authors, this explanation does not take into account that as information is encoded or remembered, these regions may, in fact, share a common code in the brain.
“We found that memory-related brain areas encode the world like a photographic negative in space,” explained co-senior author Adam Steel, a postdoctoral researcher in the Department of Psychology and Brain Sciences and a member of the Neukom Institute for Computational Sciences at Dartmouth. “And that negative is part of the mechanics that moves information in and out of memory, and between perception and memory systems.”
Three key findings about memory systems
The researchers conducted experiments to test participants’ perception and memory while their brain activity was recorded using a functional magnetic resonance imaging (fMRI) scanner. In this way, they identified an opposite push-pull coding mechanism, which controls the interaction between perception and memory areas in the brain.
The results have revealed that when light hits the retina, the visual areas of the brain respond with an increase in activity to represent the light pattern. The memory areas of the brain also respond to visual stimulation, but unlike visual areas, their neural activity decreases when they process the same visual pattern.
“We discovered that brain areas related to memory encode the world like a photographic negative in space”
The co-authors have highlighted three unusual findings from their work: The first is their discovery that a principle of visual coding is preserved in memory systems. The second is that this visual code is backwards in memory systems. “When you see something in your visual field, neurons in the visual cortex activate, while those in the memory system calm down,” says lead author Caroline Robertson, an assistant professor of psychological and brain sciences at Dartmouth.
Third, this relationship changes during recall. “If you close your eyes and remember the visual stimuli in the same space, you will change the relationship: your memory system will be driving, suppressing the neurons in the perceptual regions,” Robertson says. “Our results provide a clear example of how memory systems use shared visual information to focus and unfocus memories,” concludes co-senior author Ed Silson, professor of human cognitive neuroscience at the University of Edinburgh.
