Neuroscientists have long believed that memories are stored in the synapses, or junctions between the brain’s neurons. But UCLA neurobiologist David Glanzman subscribes to a different theory: the key to at least some memory storage, he thinks, is RNA, the cellular “messenger” that makes proteins and transmits DNA’s instructions to other parts of the cell.
Glanzman says he has the evidence to support this controversial hypothesis. As Usha Lee McFarling reports for STAT, Glanzman and other UCLA researchers claim to have transferred memories between snails through injections of RNA. Their study, published in the journal eNeuro, is eliciting both interest and skepticism among other experts in the field.
Scientists sometimes turn to snails, which have very simple brains, to try and gain insight into the more complex workings of the human mind. At Glanzman’s lab, researchers administered a series of mild electric shocks to the tails of a marine snail known as the Aplysia californica. When these snails were prodded gently, they withdrew their siphons and gills—a reflexive defense response—for around 50 seconds. But when snails that had not been shocked were tapped, they only withdrew for about a second.
As UCLA explains in a statement, the snails that had been shocked were displaying a simple type of learning known as “sensitization.” In an interview with Ian Sample of the Guardian, Glanzman likened the phenomenon “to being jumpy in the moments after an earthquake: the memory of the event induces an involuntary reflex to any loud noise.”
In the next phase of its research, the team extracted RNA from the nervous systems of the snails that had been shocked and injected it into snails that had not been shocked. Suddenly, these un-shocked snails began to withdraw their their siphons and gills for an extended period of time—about 40 seconds—after being gently touched.
“It’s as though we transferred the memory [of being shocked],” Glanzman says in the statement.
Researchers also extracted RNA from snails that had not received any shocks, and transferred it to another group of snails that also had not been shocked. The injected critters did not show any signs of prolonged contractions.
To bolster its findings, the team also added RNA from the shocked snails to Aplysia sensory neurons in a Petri dish. This produced “increased excitability” in the neurons, according to the UCLA statement, whereas RNA from un-shocked snails did not.
These results, the researchers write in the study, offer “dramatic support for the idea that memory can be stored non-synaptically.”
Glanzman is not the first to suggest that memory storage may be far more complex, and involve more mechanisms, than is commonly assumed. In 2016, for example, the Austrian scientist Patrick C. Trettenbrein pointed out a number of problems with the synapse-memory theory—but noted that “we are currently also still lacking a coherent alternative.”
Glanzman believes his study offers just that—evidence of an alternative mechanism for memory storage. “I think in the not-too-distant future, we could potentially use RNA to ameliorate the effects of Alzheimer’s disease or post-traumatic stress disorder,” he says in the statement.
But other experts are not convinced.
“It’s interesting, but I don’t think they’ve transferred a memory,” Tomás Ryan, an assistant professor at Trinity College Dublin who researches memory, tells the Guardian’s Sample. “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.”