Introducing the brain: rewiring memory (Introduction)

by David Turell , Thursday, March 03, 2022, 22:09 (1006 days ago) @ David Turell

New technique in zebrafish:

https://www.quantamagazine.org/scientists-watch-a-memory-form-in-a-living-brain-20220303/

"Researchers have now directly observed what happens inside a brain learning that kind of emotionally charged response. In a new study published in January in the Proceedings of the National Academy of Sciences, a team at the University of Southern California was able to visualize memories forming in the brains of laboratory fish, imaging them under the microscope as they bloomed in beautiful fluorescent greens. From earlier work, they had expected the brain to encode the memory by slightly tweaking its neural architecture. Instead, the researchers were surprised to find a major overhaul in the connections.

"What they saw reinforces the view that memory is a complex phenomenon involving a hodgepodge of encoding pathways. But it further suggests that the type of memory may be critical to how the brain chooses to encode it — a conclusion that may hint at why some kinds of deeply conditioned traumatic responses are so persistent, and so hard to unlearn.

***

"The amygdala is particularly responsible for associative memories, an important class of emotionally charged memories that link disparate things — like that spider in your cereal. While this type of memory is very common, how it forms is not well understood, partly because it occurs in a relatively inaccessible area of the brain.

"Fraser and his colleagues saw an opportunity to get around that anatomical limitation and learn more about associative memory formation by using zebra fish. Fish don’t have an amygdala as mammals do, but they have an analogous region called a pallium where associative memories form. The pallium is much more accessible for study,

***

"The marker protein, created in the lab of Don Arnold, a professor of biological sciences and biological engineering at USC, fluoresced under the dim laser light of a custom microscope: The challenge was “to be able to eavesdrop on something as it takes place,” but use as little light as possible to avoid scorching the creatures, Fraser said. The researchers could then see not only the location of individual synapses but also their strength — the brighter the light, the stronger the connection.

***

"Contrary to expectation, the synaptic strengths in the pallium remained about the same regardless of whether the fish learned anything. Instead, in the fish that learned, the synapses were pruned from some areas of the pallium — producing an effect “like cutting a bonsai tree,” Fraser said — and replanted in others.

"Previous studies have sometimes suggested that memories can form through the addition and deletion of synapses — but this real-time and large-scale visualization of the brain suggests that this method of memory formation may be much more significant than researchers realized. Though it’s not definitive proof, “I think it provides compelling evidence” that this could be a major way the brain forms memories, said Tomás Ryan, a neuroscientist at Trinity College Dublin who was not involved with the study.

"To reconcile the results of their new study with their initial expectations of memory formation, Fraser, Arnold and their team hypothesize that the type of memory might direct how the brain chooses to encode it. These “associative events that we’ve looked at might be the strongest sort of memories,” Fraser said. For the fish they’re do-or-die, so “it’s not too surprising that you might encode these strong memories in a very strong way.”

"But what’s appropriate for locking in fear-ridden memories may not be best for more mundane types of memories. When learning to pronounce somebody’s name, you probably “wouldn’t want to be yanking synapses out of your brain and adding new ones,” Fraser said."

Comment: we see other of my predictions validated. Simple organisms complexify brains just like our brains do. Complexification in brains was evolved long before humans appeared, destroying dhw's contention that evolution is a disconnected process. Biological processes going back to Archaea support human life. Every twig on the bush of life uses various processes from the past.