Why we keep tampering with snails’ memories
According to viral news stories, scientists have managed to erase and transfer the memories of snails, and the same techniques could be applied to humans. What’s actually going on here?
I recently stumbled across this tweet:
It gave me a good giggle, but I was sceptical of that original claim. When you see science news that looks a little too quirky and shareable, you should ask if the research has been twisted. It’s also wise to question any suggestion that because something worked on an animal, it’ll work on humans too — especially if we’re talking about an animal as different from us as a snail.
I went hunting for sources, beginning with a quick search for “snail memory modification”. To my surprise, I realised I was going to have to be more specific. In another widely shared story, scientists had apparently managed to transfer memories from one snail to another, causing them to remember something they’d never experienced.
I had two questions: 1) How well do these claims hold up? and 2) Why do we keep messing with snails’ memories, anyway?
Snails make good test subjects in memory research for several reasons. Firstly, they have large neurons, which makes it easier to pinpoint where memories are stored. It’s also possible to observe neural signalling in snails while they’re still alive, allowing researchers to get a more realistic impression of how snails’ nervous systems really function.
While a complex web of factors can influence human memories and behaviour, snails are far simpler. It’s easy to regulate their experiences, and they respond to those experiences in a straightforward way. Poke a snail with a probe, and it’ll shy away.
The final and most basic advantage of using snails in research is that, well, they don’t have rights. Animal research is a contentious issue, and it’s restricted to some extent in most countries. But these restrictions don’t usually apply to invertebrates, except crustaceans and cephalopods. You’re free to do whatever you like with molluscs. The only time most of us mourn the fates of snails is when we’ve accidentally stepped on one.
The memory erasure research referenced in the Motherboard tweet was carried out by Hu and colleagues.
This study generated lots of excitement. Most headlines went with similar wording to the tweet. Scientists Have Managed To Erase Memories In A Snail’s Brain, said IFLScience. Futurism opted for Scientists Selectively Erased Memories In Snails — Are We Next? I could go on. These stories were shared on social media, where people wondered whether Eternal Sunshine of the Spotless Mind or Black Mirror-style futures were around the corner.
But after reading the original paper for myself, I think these headlines are stretching the truth.
In the study, sensory and motor neurons were isolated from the marine snail Aplysia californica. Sensory neurons are nerve cells that detect external signals, like heat or light, while motor neurons send commands from the nervous system to the body to produce responses to these signals. The researchers produced cultures, each containing two sensory neurons and one motor neuron.
After a few days, the neurons formed synapses (connections). One sensory neuron was stimulated to induce an associative memory while the other was stimulated to induce a non-associative memory.
Associative memories are formed when we’re conditioned to connect two unrelated stimuli. For example, you might give your dog a treat for coming to you when called, teaching the dog to associate obedience with tasty food.
Non-associative memories are formed in response to only one stimulus, with no link to consequences. The two main forms of non-associative learning are habituation, in which an organism becomes less sensitive to a stimulus with repeated exposure, and sensitisation, in which it becomes more sensitive. Imagine how someone who lives next to a railway line might get used to the sound of trains, or how the persistent dripping of a tap could get more annoying as you try to sleep.
The researchers analysed the strength of the connections for the associative and non-associative memories. They found that a different form of a Protein Kinase M (PKM) molecule was responsible for maintaining the strength of the connection depending on the type of memory. By blocking one of these molecules, one memory could be erased without affecting the other.
You can see by now why “Scientists just erased certain memories from a snail’s brain” is misleading. Firstly, snails don’t have brains. And no snails actually had their memories wiped in this study — only isolated neurons were involved. (That’s just a petty gripe, though, because a different memory erasure study was performed on live snails. It’s possible.)
But my most crucial point is that the researchers learned how to erase certain types of memory (i.e. associative or non-associative). What they didn’t learn was how to expunge anything as specific as, say, the experience of eating a lovely lettuce leaf.
Applications of memory erasure
While combing through responses to this study, I saw one blogger declare it had obviously been carried out to develop a method of mind control. Thankfully, that’s not it.
The eventual goal of memory erasure research is to treat conditions like PTSD and anxiety by removing memories that cause unhelpful fear responses.
We may be able to take advantage of a flaw in the way our memories work. When we retrieve a memory, it becomes vulnerable to alteration. In fact, the more we recall a memory, the more its detail fades away and is replaced with the general gist of the experience. However clear your childhood memories seem, they’ve probably evolved quite a bit over time.
After we recall a memory, our brains have to restabilise it. Theoretically, if someone recalls a memory and then has the restabilisation process disrupted, the memory could be impaired, i.e. through interference with the relevant PKM molecule. Because fear responses tend to be associated with non-associative memories, Dr Samuel Schacher, a co-author of the paper we’ve just discussed, suggests we can target these connections while keeping helpful associative memories safe.
“One focus of our current research is to develop strategies to eliminate problematic non-associative memories that may become stamped on the brain during a traumatic experience without harming associative memories, which can help people make informed decisions in the future, like not taking shortcuts through dark alleys in high-crime areas,” said Dr Schacher.
There are a couple of problems with this idea, though. There’s no guarantee the induced amnesia would last, since weakened synapses can grow stronger again. And I’m not convinced that the situation is as clear-cut as “Associative memories are good and non-associative memories are bad”. Not all non-associative memories are linked to fear.
Besides, would we really want to lose all the memories that scare us? We evolved fear responses because they were helpful. Remembering the upsetting things that have happened to us can protect us in future.
Of course there are fears and memories that certain people would be better off without, but we’re a long way off knowing how to target them specifically. Until then, attempts to erase those memories are likely to cause more harm than good.
Let’s move on to our second snail memory study. In a paper published in 2018, Bédécarrats and colleagues reported that they’d managed to transfer memories from one snail to another.
A group of A. californica were subjected to sensitisation training in which their tails were repeatedly shocked. Trained snails exhibited a strong siphon-withdrawal reflex (SWR) — a retraction of the tube through which water flows.
The researchers then extracted RNA from the central nervous systems of the trained animals and a control group. The RNA was injected into untrained snails. When poked with a soft probe, snails that had been injected with RNA from the trained snails exhibited enhanced SWRs. It seemed as though the trained snails’ memories of the shocks had been transferred to the untrained snails via their RNA.
Again, the end goal isn’t just to bully snails (or to develop mind control techniques). Lead author David L. Glanzman hopes we may be able to identify RNA linked to memory disorders. “If we can identify some of the RNA that produces learning like alterations,” he said, “it is possible we could use that knowledge to create new and more effective treatments.”
If nothing else, these findings suggest that we still have a great deal to learn about memory storage. We’ve always assumed memories are exclusively stored in the brain, but this study suggests we could have some memories floating around in our RNA too.
But again, we shouldn’t get overzealous about these findings. The RNA encoded something that made the snails flinch, but it wasn’t necessarily a memory.
Memory researcher Tomás Ryan told the Guardian, “It’s interesting, but I don’t think they’ve transferred a memory. This work tells me that maybe the most basic behavioural responses involve some kind of switch in the animal and there is something in the soup that Glanzman extracts that is hitting that switch.”
In summary, we’ve still got a lot left to learn about how our memories work. But luckily, snails are here to help.