Memory and perception use a common code in the brain, research suggests, which could shed light on the challenges faced in Alzheimer’s disease.
Conventional views of brain organisation assume that externally oriented, perceptual areas and internally oriented, mnemonic areas use different coding principles.
The neural code that structures how visual information is processed in the brain is believed to represent the world retinotopically—according to how light hits the retina.
As the information moves towards memory areas, this has then been thought to be replaced with an abstract format.
Writing in Nature Neuroscience, researchers now report that retinotopy is the coding principle that straddles both areas, structuring their interaction.
“Our results provide a clear example of how shared visual information is used by memory systems to bring recalled memories in and out of focus,” explained co-first author Ed Silson, PhD, a lecturer in human cognitive neuroscience at the University of Edinburgh.
Silson and team recorded brain activity during perception and memory experiments in 17 volunteers using functional magnetic resonance imaging.
This showed an opposing coding mechanism that governed the interaction between perceptual and memory areas in the brain, in a push-pull manner.
When light fell onto the retina, visual areas of the brain responded by increasing activity in a representation of the pattern of light. While memory areas of the brain also responded to visual stimulation, their neural activity decreased for the same visual pattern.
“When you see something in your visual field, neurons in the visual cortex are driving while those in the memory system are quieted,” explained senior author Caroline Robertson, an assistant professor in psychological and brain sciences at Dartmouth College.
“If you close your eyes and remember that visual stimuli in the same space, you’ll flip the relationship: your memory system will be driving, suppressing the neurons in perceptual regions.”.
Co-first author Adam Steel, PhD, a post-doc researcher in the same Dartmouth department, added: “We found that memory-related brain areas encode the world like a ‘photographic negative’ in space.
“And that ‘negative’ is part of the mechanics that move information in and out of memory, and between perceptual and memory systems.”
The researchers believe that functional ties between the inverted retinotopic code at high-level brain areas approaching the cortical apex and the positive retinotopic code in perceptual areas may be crucial for scaffolding communication between memory and perception.
They now plan to investigate how the push-pull dynamic between perception and memory could contribute to challenges in clinical conditions such as Alzheimer’s disease.
