To most of us, memories are intangible, like floating photo albums existing only in the mind. However, some scientists argue that some memories exist physically, in the form of biochemical changes called engrams. In a study published Monday in eNeuro, scientists show that engrams are unexpectedly encoded in physical strings of ribonucleic acid, or RNA. Perhaps more spectacularly, it seems that RNA can transfer memories from one individual to another.
If it’s been a while since high school biology, remember that RNA, like its more well-known cousin DNA, is a chain of nucleic acids that carries information cells need to create proteins, regulate themselves, and carry out biochemical reactions. The University of California, Los Angeles scientists report in the new paper that they were able to shift memories from trained sea snails to untrained sea snails, all by injecting them with the former’s RNA.
While the concept of physically transferring memories from one entity seems as fictional as the memory-preserving Penseive in Harry Potter, it’s actually been studied enough that there are several theories about how it works. Prior to this study, scientists studying engrams generally accepted that long-term memory is housed in synapses, the connections between brain cells. In the new study, however, the study authors assert their experiment proves that memories are stored in the nuclei of neurons, where RNA is stored and produced. This new study argues that changes in gene expression in non-coding RNAs underlies the memory storage process.
In the study, the team led by UCLA biologist David Glanzman, Ph.D. took California sea hares (which, despite the name, are snails of the Aplysia genus), implanted wires into their tails, and administered a series of electric shocks. After a “training period,” the snails eventually learned to fear the wires, contracting their gills defensively for about 50 seconds when the shock-inducing tool was brought out. The group that wasn’t shocked only defended themselves for about one second after being hooked up to wires.
The process, Glanzman promised the BBC, didn’t cause long-term harm: “These are marine snails and when they are alarmed they release a beautiful purple ink to hide themselves from predators. So these snails are alarmed and release ink, but they aren’t physically damaged by the shocks,” he said.
The shocks, however, did appear to leave a physical mark on the snails’ RNA.
The team extracted RNA from the experimental group of snails and inserted it into a new batch of snails that hadn’t been exposed to the shocks. When they were hooked up to wires, these new snails, plump with the RNA of their frightened kin, responded with the same defense mechanism for 40 seconds. This, says Glanzman, is evidence that the fear memory from the first group was transferred to the second through its RNA.
Not all memories are thought to be stored in this way — at least as far as scientists can tell. The behavioral memories this study focused on are “a form of non-associative long-term memory,” the scientists point out, concluding that the results “indicate that RNA is sufficient to generate an engram for long-term sensitization in Aplysia and are consistent with the hypothesis that RNA-induced epigenetic changes underlie memory storage in Aplysia.”
It’s too early to draw any conclusions about human memory storage from the results in the snails, as Cardiff University memory researcher Seralynne Vann, Ph.D. pointed out to The Guardian on Monday. Glanzman, nevertheless, argues his team’s findings raise the possibility that RNA could be used to modify memory. Whether or not this means that humans of the future will be able to edit their most embarrassing moments remains to be seen — but we can keep our fingers crossed.