Can we transfer memories from one living being to another?

David Glanzman expects to see a lot of surprise and skepticism in response to the study discussed here. He and his colleagues at the University of California, Los Angeles have managed to transfer memories from one sea snail to another. Their experiment raises questions about our conception of memory, something which was little debated in the (neuro) scientific community until now. Let’s take a look at why this transfer of memory in mollusks should be approached with care.

Before delving into the experimental details and the debate they provoke, it should be noted that the research conducted by Glanzman focuses on the study of the engram, a biological trace of memory in the brain. Currently, it is widely accepted that long-term memories are recorded through a strengthening of connections, or synapses, between groups of neurons that participate in encoding our life experiences. In addition, recent work carried out with marine mollusks has shown that, in these species, long-term memory could be restored after amnesia thanks to a process involving ribonucleic acid (RNA). RNA is a molecule found in virtually all living things, and plays an important role in the formation of long-term memories.

For their experiment, the scientists “trained" sea snails (Aplysia californica) as follows: they gave them light electrical shocks to trigger a withdrawal reflex in these gastropod mollusks. The “conditioning” was apparently successful: after the first shock, the contraction lasted about a second, but after about ten more shocks, it lasted for 50 seconds. It’s as if the sea snail had “learned” to defend itself. Next, the researchers collected ribonucleic acid from the nervous systems of the “sensitized” mollusks and injected it into 7 “naïve” mollusks.

What happened to the individuals in this group? Though they had never been "conditioned," they still reacted very similarly to the electric shocks, contracting their tails for an average of 40 seconds. “It’s as thought we transferred the memory,” exclaimed Glanzman. His team also observed that the RNA extracted from the “trained” snails increased the excitability of sensory neurons (grown in Petri dishes) from snails that had never been subjected to electric shocks.

Glanzman and his colleagues know that their study challenges the idea that memory is stored in the synapses. For these scientists, memories are stored in the neuron nucleus (where RNA is synthesized). In this case, the RNA would tell the DNA which genes to activate or deactivate, and these “epigenetic” modifications would be responsible for storing memories. The authors also point out that the sea snail is an excellent model for studying brain and memory because their cellular and molecular processes seem to be very close to those of humans (even if snails only have about 20,000 neurons in their central nervous system compared to 100 billion in humans).

Glanzman is quick to discuss the possibility of generalizing the findings to humans: “In the not-too-distant future, we could potentially use RNA to ameliorate the effects of Alzheimer's disease.” For the time being, and in the interest of scientific caution, similar studies will have to be carried out to strengthen or disprove this hypothesis.
Source: Bédécarrats A., Chen S. , Pearce K, Cai D., Glanzman D. RNA from Trained Aplysia Can Induce an Epigenetic Engram for LongTerm Sensitization in Untrained Aplysia, in eNeuron, May 2018

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