Do you envy someone's memories? Seeing your favorite artist live, or time with a loved one now gone, perhaps? One day, perhaps we will be able to copy those memories into our brains. It's an unimaginably long road there, but a new paper might be considered the first step as scientists have successfully "transferred" memories from snail into another.
UCLA researchers gave electric shocks to the tails of Aplysia marine snails, not strong enough to harm them, but sufficient to cause mild pain and trigger the snail's withdrawal response into its shell. The shocks were delivered in batches of five, 20 minutes apart, followed by another set of five a day later.
Snails primed in this way were understandably more wary of the world, and when the team tapped on their shells would withdraw for an average of 50 seconds. Unshocked Aplysia counterparts spent just a second or so on their shells in response to similar taps.
Such a study could be compared to Pavlov, but senior author Dr David Glanzman took it somewhere very different. Working on a theory memories are stored in epigenetic modifications to DNA, he extracted nervous system RNA from each group of snails. The RNA from those given the shocks was injected into unshocked snails, while that from the snails that had not been primed was given to a control group.
Snails getting RNA from their shock-receiving counterparts responded to taps almost as defensively as those that had received the shocks themselves, withdrawing for 40 seconds on average. The control group were unaffected, the team report in eNeuro proving the behavior was not an effect of the RNA transfer process, but of the memories the RNA carried.
"It's as though we transferred the memory," Dr Glanzman said in a statement.
We still don't understand how memories are recorded, particularly the much more complex experiences of color, sound, and taste. Nevertheless, the work provided some hints. For one thing, when the RNA was transferred to snail neurons in Petri dishes, the operation was found to increase the excitability of sensory neurons, which convert external stimuli to electrical impulses, but not movement-controlling motor neurons.
Moreover, the RNA from sensitized snails methylated the recipient neuron's DNA, suppressing gene expression and matching what occurs in the DNA of snails that had experienced the shocks directly, supporting the epigenetic memory theory.
The findings contradict the dominant synaptic theory of memory, which Glanzman has previously challenged by interrupting protein synthesis in Aplysia, affecting memories in the process. "If memories were stored at synapses, there is no way our experiment would have worked," Glanzman said. He doubts this is something that would have changed after our evolutionary path separated from mollusks, although we have around 5,000 times as many neurons as Aplysia do.