How does our brain encode visual memories?

Memory has always fascinated scientists. Often, sitting thousands of miles away, people can easily recall the colour of their kitchen walls, living room layout, interiors of their go-to restaurant and decor of the corner shop they frequently visit. However, how this information is encoded by the brain has been a mystery for neuroscientists.

In a new study, led by researchers from Dartmouth College, researchers have identified a neural coding mechanism that allows the transfer of information between perceptual regions to memory areas of the brain. The results were published recently in the journal Nature Neuroscience.

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For long, the classical understanding was that perceptual regions of the brain represent the world "as it is," with the brain’s visual cortex representing the external world based on how light falls on the retina, "retinotopically," a press statement from the university explains. 

It was thought that the brain’s memory areas represent information in an abstract format, without the details about its physical nature. However, the new study points out that this explanation does not consider that as information is encoded or recalled, these regions could share a common code in the brain.

In this study, the researchers found that memory-related brain areas encode the world like a 'photographic negative' in space, co-lead author Adam Steel elaborated in the statement. "And that ‘negative’ is part of the mechanics that move information in and out of memory, and between perceptual and memory systems," Steel added in the statement.

The findings revealed that when light hits the retina, visual areas of the brain increase their activity to represent the pattern of light. Memory areas of the brain also respond to visual stimulation, but their neural activity decreases when processing the same visual pattern, the statement explained.

The researchers found that a visual coding principle is preserved in memory systems and this is upside down. This relationship flips when recalling a memory. "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," senior author Caroline Robertson said in the statement.

Hence, the results show how shared visual information is used by memory systems to bring recalled memories in and out of focus, the researchers wrote in the statement.

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