In one of the most progressive memory studies to date, researchers from the University of California in Los Angeles (UCLA) have managed to transfer memories between sea snails, ScienceDaily reports.
The "memory transplant" was achieved through ribonucleic acid (RNA) injections and provides new tantalizing clues regarding the memory trace — also known as an engram, the presumed physical substrate of memory.
This groundbreaking experiment began with training a group of sea snails belonging to the Aplysia californica species, colloquially known as the California sea hare. The UCLA team applied mild electric shocks to the creatures' tails in order to provoke a defense mechanism — a withdrawal reflex in which the snails contracted to protect themselves from harm.
Senior study author David Glanzman, from UCLA's Department of Integrative Biology and Physiology, pointed out that the snails used in the experiment were not hurt in any way.
"These are marine snails and, when they are alarmed, they release a beautiful purple ink to hide themselves from predators," Glanzman said in a statement.
"So, these snails are alarmed and release ink, but they aren't physically damaged by the shocks," he explained.
In the experiment's next step, the researchers gauged the withdrawal reflex by tapping both snails that had been trained, or sensitized, in this way and a control group that didn't receive the shock treatment.
According to the BBC, the team observed that sensitized snails had a defensive contraction of up to 50 seconds, whereas the specimens that weren't familiar with the electric shock only contracted for about a second.
Once this initial phase of the experiment was completed, the researchers extracted RNA from the sensitized sea hare snails and injected it into untrained specimens.As it turned out, the RNA samples retained the memory of the electric shock, causing the untrained snails to exhibit a defense mechanism that lasted almost as long as that of the donor snails.
In a statement for The Guardian, Glanzman commented on the nature of the experiment, noting that the type of memories that were transplanted from one snail to another was crucial to the success of the procedure.
"What we are talking about are very specific kinds of memories, not the sort that says what happened to me on my fifth birthday, or who is the president of the United States."The experiment revealed that the recipients of the "memory transplant" contracted for about 40 seconds when tapped, suggesting that the RNA injections had transferred the memory of the electric shock to the unsensitized snails.
In a study published today in the journal eNeuro, the UCLA team argues that these results refute the general consensus that long-term memory is stored in the brain synapses that connect cerebral cells.As Glanzman points out, if that theory were true, then the experiment wouldn't have succeeded. Instead, his team suggests that long-term memories are actually encoded in RNA molecules, just like it happened in the case of the sea snails.
However, Glanzman's unique experiment was met with skepticism by some scientists. Tomas Ryan, who studies memory at Trinity College Dublin in Ireland, opined that, as impressive as their study may be, the UCLA team didn't actually transfer a memory, but rather a basic behavioral response that triggered the defense mechanism in the untrained snails.
At the same time, Prof. Seralynne Vann from Cardiff University in the U.K. made an interesting point about the chances of applying a similar technique in the study of human memory.
"While the Aplysia is a fantastic model for studying basic neuroscience, we must be very careful in drawing comparisons to human memory processes, which are much more complex," he noted.