Introducing the brain: memory depostion is scattered (Introduction)

by David Turell , Wednesday, February 09, 2022, 19:55 (1016 days ago) @ David Turell

A summary of new studies:

https://www.quantamagazine.org/new-map-of-meaning-in-the-brain-changes-ideas-about-memo...

"But in recent years, researchers have repeatedly found subtle yet significant differences between visual and memory representations, with the latter showing up consistently in slightly different locations in the brain. Scientists weren’t sure what to make of this transformation: What function did it serve, and what did it mean for the nature of memory itself?

"Now, they may have found an answer — in research focused on language rather than memory.

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"The finding, published last October in Nature Neuroscience, suggests that in many cases, a memory isn’t a facsimile of past perceptions that gets replayed. Instead, it is more like a reconstruction of the original experience, based on its semantic content.

"That insight might help to explain why memory is so often such an imperfect record of the past — and could provide a better understanding of what it really means to remember something.

***

"They found remarkably consistent patterns in all the participants — patterns that formed a generalized map of visual meaning. It confirmed the identity of some regions of the visual cortex that were already known from earlier research, such as areas selectively responsive to faces or places. But it also turned up hundreds of other selective patches for the first time: regions that responded to images of animals, family members, indoor scenes, outdoor scenes, people in motion, and more.

***

"So Huth called up the data from his 2012 vision experiments and saw that in this place-selective area of the cortex, the back part responded exclusively to place-related images. When he looked in areas closer to the front, both place images and place words were represented — until, at the boundary of the region, only words evoked brain activity, just as he’d seen when he was toying around with his 2016 visualization. There seemed to be a gradual, continuous shift from visual representations of places to linguistic representations over just a couple of centimeters of cortex.

“'It was surprisingly neat,” Huth said. “This was the exciting ‘aha’ moment, seeing this pattern pop out.”

"To test how systematic the pattern might be, Sara Popham, then a graduate student in Gallant’s lab, developed a statistical analysis for the team that looked for these gradients along the border of the visual cortex. They found it everywhere. For every one of the hundreds of categories studied in the experiments, the representations aligned in transition zones that formed a nearly perfect ribbon around the entire visual cortex. “There’s a match between what happens behind the border and what happens in front of the border,” Gallant said.

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"The pattern was also systematic across individuals, appearing over and over in each participant. “This real boundary in the brain seems to be a general organizing principle,” said Adam Steel, a postdoctoral fellow studying perception and memory at Dartmouth College.

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"In hierarchical models of visual processing, the brain first extracts specific features such as edges and contours, then combines those to build more complex representations. But it’s been unclear how those complex representations then get increasingly abstract. Sure, visual details might get pieced together to create an image of, say, a cat. But how does that final image get assigned to the conceptual category of “cats”?

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"Over the past year, several new studies — including research by Bainbridge, Baker, Steel and Caroline Robertson of Dartmouth College — have reinforced that finding by directly comparing people’s brain activity as they looked at and later recalled or imagined various images. In each case, a systematic spatial transformation marked the difference between the brain’s sensory and memory representations. And the visual representations appeared just behind the associated memory ones — just as they had in Huth’s language-based study.

"Like that study, this one seemed to indicate that perception and memory are also deeply entangled. “It doesn’t make sense to think of our memory system as a totally separate workspace,” Baldassano said.

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"Huth’s work provides new insights into the nature of that transformation. Perhaps memory isn’t as visually driven as we thought. Maybe it’s more abstract, more semantic, more linguistic. “We often have this impression that we have these fantastic visual representations of things,” Baker said. “You feel like you can see it. But maybe you can’t.”

"To Kuhl, that makes sense. After all, “we know that when we’re imagining something or remembering something, it’s distinct from actually seeing it,” he said. What we see in our mind’s eye might be a reinterpretation of a remembered scene or object based on its semantic content rather than a literal replay of it. “We’re so fixated on using perceptual experience as a template. But I think that has blinded us a little bit.'”

Comment: we see our brain cane initially prepared to organize itself. What were all these regions doing 315,000 years ago? Some regions were quite active and some not so much. Deny the brain came unprepared for future use.