Memories are made by experience. For instance, you know you like donuts because you've had possibly hundreds of delicious donuts in your lifetime. But what if you could have fond memories of donuts, not because you'd ever had one before, but because somebody slipped you a transplanted donut memory.
No, Jim Carrey isn't in this movie. And it's not a movie, it's science.
A team of researchers at UCLA has been the first to successfully transplant memory from one organism into another. The study, published in the May 14, 2018 issue of eNeuro, the online journal of the Society for Neuroscience, reports their success in using the genetic molecule ribonucleic acid (RNA) to transplant a memory from one marine snail (Aplysia californica) into another.
The research team gave the memory donor snails a series of mild electric shocks to the tail over the course of two days, and when threatened in this way, the snails retracted the fleshy flaps on the sides of their bodies called parapodia. Afterward, when the researchers so much as tapped these snails, they withdrew their parapodia for around 50 seconds. And let's be frank: These sea snails aren't particularly smart — they don't even have the type of nervous system that involves a brain — but the trauma of getting repeatedly shocked on the butt led them to become "sensitized," which is a simple type of memory. A control group of snails that never received the series of shocks only retracted their parapodia for about a second after being tapped by the researchers.
Here's where it gets weird. Next, the scientists extracted RNA from the sensitized snails and injected it into seven snails that hadn't received shocks. Afterward, when tapped, these snails pulled in their parapodia for an average of 40 seconds.
"It's as though we transferred the memory," David Glanzman, senior author of the study and professor of integrative biology, physiology and neurobiology at UCLA, said in a press release.
The researchers went on to put RNA from shocked snails into Petri dishes containing bundles of neurons from snails that didn't receive the shocks. They found that this resulted in the neurons getting extremely excited when bathed in a chemical messenger that suggested an electric shock to the butt. Neurons from the unsensitized snails didn't become nearly as excited.
The research team concluded that this ability for memory to be transferred from one snail to another through RNA suggests we know less than we think about where memories are stored. It's been assumed until recently that they are kept in synapses, of which each neuron contains thousands.
"If memories were stored at synapses, there is no way our experiment would have worked," Glanzman said.
Instead, he suggests they might be kept in the nucleus of neurons.