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Recent Experiment on Snails May Have Just Called Into Question Everything We Thought We Knew About Where Memories Are Stored

Experiments with marine snails suggests that some memories might be held in RNA, and not neurons.

A researcher at the University of California-Los Angelesmay have discovered more about where memories are stored, and it could have major implications for neuroscience. Daniel Glanzman, a professor of neurobiology at UCLA made the discovery while working with his usual subject: the California sea hare, a 12-inch marine snail.

In the latest study, Glanzman gave a group of snails a mild electric shock. When snails feel threatened, they retract their frills and spout, so after a few shocks, the snails were sensitized, and retracted for about 50 seconds. Snails that have not received shocks typically retract for as little as one second.

Next, Glanzman removed the RNA — the “messenger” that transports information from a cell’s genome to every other part — from the sensitized snails’ neurons and transferred it to snails that had never been shocked. But when the unshocked snails’ tails were prodded, as though electrodes were being attached, the snails retracted for about 40 seconds, suggesting that the RNA transfer had also transferred the recollection of being shocked and the defense reaction it provoked.

“It feels like I’m way out on a limb, frankly,” Glanzman said. “[But] if memories were stored at synapses, there is no way our experiment would have worked.”

Broadly speaking, neuroscientists believe that memories are stored in synapses, the structures that allow separate cells to communicate with each other, although most allow that our understanding of brain function is in its infancy. And it’s far from certain that a similar RNA transfusion into human neurons would produce identical results.

“It’s interesting, but I don’t think they’ve transferred a memory,” said Trinity College Dublin assistant professor Tomás Ryan, who specializes in memory engrams. “This work tells me that maybe the most basic behavioral responses involve some kind of switch in the animal and there is something in the soup that Glanzman extracts that is hitting that switch.”

But fresh ideas are often needed inconservative fields like neuroscience. Scientists have begun to believe that RNA fulfills more functions than just a messenger, and Glanzman’s study offers another possible function.

Because the snails have large neurons, they’re easy to experiment with, so Glanzman has focused on them for several years. He says that their neurons are similar to human neurons, but snails have far fewer: just 20,000 compared to humans’ 100 billion. Other scientists researching memory in mammals have found that RNA plays a crucial role in thebrains of rats and mice. In their brains, it appears that RNA influences the chemical tags on DNA, determining which genes will be switched on or off.

It’s not the first time that memories can be transferred through physical absorption. In the 1960s, researchers trained a group of flatworms to respond to light, then chopped them up and fed them to other flatworms that had not been trained. The untrained worms responded to light in the same way as the trained flatworms had. The results of those studies were difficult to replicate, but Glanzman’s work with snails suggests that more investigation in this area may prove fruitful.