Scientists watch a memory form in the brain of a living fish | Hacker News Reader

Scientists watch a memory form in the brain of a living fish

quantamagazine.org

129 pointsdoetoe31 comments

In fish...

"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."

This is a very counter intuitive. So there are existing neural connections (formed somehow previously...) and new memories form by pruning these connections? Crazy

Not crazy, think of how quake levels are made with brushes, the brushes are "filled" solid and you carve out empty space to make paths and structures.

Still crazy that evolution has chosen it.

Crazy nonetheless that evolution has chosen it.

Ok, we've infished the title above. Thanks!

That's consistent with the way, children react to languages and faces. When we are born, we are open to all languages. When we grow up, we only remain receptive to the language structures to which we had been exposed previously. Of course it's always possible to learn a new language, but it is easier with previous exposure.

(citation needed)

I don't think it is counter intuitive (maybe if you hold a strong opinion, it is.) There's a growing body of evidence that brains, to some degree, learn by removing connections, and in some cases, add connections elsewhere.

I think part of learning is, that we have some general idea about something, but it turns out to be inaccurate, so we need to specialize it (and get rid off the old connection.) I'm speculating though.

I'm a bit confused by the "replanted in others" part though. I'd assume, overall, there is a net loss of synapses when learning (and hence learning becomes more difficult as we age - there just isn't enough entropy to prune away.)

And Discussion https://news.ycombinator.com/item?id=29940435

The article also has some older references - the idea isn't new.

Artificial neural networks have something similar, called the lottery ticket hypothesis

I'm not sure it is quite comparable, as the lottery hypothesis postulates that for every Neural Net with n connections/weights, there is one with n-1 connections, that retains its accuracy. So it doesn't learn by pruning, just becomes more efficient by being smaller. That's at least how I understood it.

Your thing would imply a 0 connected neural net could compete with GPT3. I quote

The Lottery Ticket Hypothesis: A randomly-initialized, dense neural network contains a subnetwork that is initialised such that — when trained in isolation — it can match the test accuracy of the original network after training for at most the same number of iterations. - Frankle & Carbin (2019, p.2)

Yeah, that's why it is merely a hypothesis. I think the Lottery Ticket hypothesis goes further and states that this subnetwork also has a subnetwork which matches test accuracy, up to some degree. Else it wouldn't be interesting. Of course there must be a limit...

The interesting bit is that you don't need to tweak the subnet, only remove the other noisy connections. If you remove capacity, at some point test accuracy needs to go down. The hypothesis is about the idea that we maybe don't "train" the weights, we "find" them, not about unlimited nesting (as far as I understand it, but I have high confidence. Happy to be proven wrong tho)

Subtractive sculpture:

https://artistryfound.com/what-is-subtractive-sculpture/

I wonder if this means that learning useless information is extra counterproductive in that it may make it difficult to learn other things because you’ve pruned some neutral connections?

Maybe instead of adding "new knowledge" our brain works by "removing bad candidates".

That’s counter intuitive (at least for you) because in modern society it’s customary to think that people are born tabula rasa and then “it’s all a social construct”. Perhaps we are indeed born with innate preferences, biases, and default sexual orientations …

Makes me think of some ancient philosophical theories that all learning is the uncovering of latent memory

I recall the experience of a blind adult getting surgery that allowed for vision, and describing the process of learning visual information gave some idea of what infants experience; first it is all brightness, or darkness, then very vague shapes and primary colors, eventually honing in on discrete objects and hues.

It makes more sense that, without any context, our brain can't just "add" a color to its repertoire, but must interpret some data within the context of existing 'thought'. Some things may be literally unimaginable without a framework of existing memories and experiences, or only possible through some recursive process "Oh so 'a' is 'like' xyz, that makes sense".

>While a developing mammalian brain grows by just getting bigger — “inflating like it’s a balloon” — the zebra fish brain almost turns itself inside out “like a popcorn kernel, so those deep centers are up near the surface where we can image them.

Makes me wonder: How big is the hidden cost of destroying rain forests and other habitats? Every species that we lose is the loss of genetically encoded knowledge that could be very useful at some point.

Could we protect the environment by making investment fonds eligible to the profits from genetic knowledge on the territory they own?

> How big is the hidden cost of destroying rain forests and other habitats?

Incalculable, since we have no idea what we're losing?

Super cool, they added fluorescent proteins that activate when the neurons fire and did it in a Zebrafish which is transparent so they could literally watch the memories forming. Interesting also they wanted to keep the light as low as possible to not scorch the little guys.

Are they not like rats where they "sacrifice" them regardless of the testing done?

> Are they not like rats where they "sacrifice" them regardless of the testing done?

The protocols for lab animal euthanasia are incredibly humane. I don't mean to criticize you, but I think perspective can help anyone come to terms with this.

When you think about what nature itself does to capture energy, that's at times incredibly savage and brutal. Gazelle on the Savannah being hunted and eaten alive by lions, rodents in the field being picked off by eagles, wasps laying eggs in live prey, fungi infecting the brains of animals and causing them to be eaten.

Lab research may seem macabre, but it doesn't hold a candle to nature itself. And our lab research seeks an end of human disease and suffering.

Even if we collectively decided that every human must behave in a way that doesn't kill any other life, one day our sun will burn out and all life on this planet will end.

Inflicting unnecessary pain during testing would be counter-productive to the testing goal.

I've always wondered if the fluorescent markers are visible to the fish and whether that might change their behaviour during experiments especially if it is a group interaction with other specimens who are not similarly modified.

That doesn’t sound much like memory formation though, per se. Sounds more like adaptation / improved emotional regulation, which (less surprisingly) requires major rewiring.

https://en.wikipedia.org/wiki/Synaptic_pruning

I'm more concerned about the mechanism current memories being modified in actual developed cognition, regardless of age/location. Does it pass the "sniff test" if animals can't distinguish the difference?

Why didn't they try to create a good memory too, just to see if there appeared to be a difference in how it was created or stored?

Looks super cool. I read about Neural Pathways in grad school, and seeing all that theory in action feels great.

Very nicely done. This is great research. Technical, creative, and substantive. Congrats to the whole team.

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