Erasing memories of scorned lovers is no longer just a movie trope popularized in Eternal Sunshine of the Spotless Mind. A new study of snail neurons suggests it's possible to wipe out specific memories in snails, and scientists think that a drug could be developed to do the same with humans in the future.

Long-term memories are moderated by synapses, essentially tubes that allow one neuron to pass along a signal to another. The properties of the synapses can increase or decrease in strength, and that's "responsible for the maintenance of the memory," wrote co-author Samuel Schacher, a professor of neuroscience in the Department of Psychiatry at the Columbia University Medical Center, in an email. According to him, "we were able to reverse long-term changes in synaptic strength at synapses known to contribute to different forms of memories."

Snail neurons. The activity of the PKM molecule is blocked. Image: Schacher Lab/Columbia University Medical Center

In this study, published today in Current Biology, researchers from McGill University and Columbia used a marine snail called Aplysia and selectively erased certain kinds of long-term synaptic memories. They found that the strength of associative and non-associative memories are maintained by two different types of Protein Kinase M (PKM) molecules, and by blocking one of those molecules, they could decide which memory to block. "Looking at neural circuits, especially the identity of specific cells that encode a memory are not that simple, let alone examining whether they are changing in strength," wrote Schacher. "So in this study we were able to reverse long-term changes in synaptic strength at synapses known to contribute to different forms of memories that last several weeks."

At this point, they're not sure if the erased memories will stay erased permanently.

One can imagine that wiping out selective memories could really help someone suffering from anxiety, PTSD, or some other trauma related to past events. But snails aren't people, and plenty of research in lab animals doesn't translate well to humans. Still, researchers say their findings open up the opportunity for a drug to be developed to erase memories that trigger anxiety and post-traumatic stress disorder without impacting other big, important memories.

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In a traumatic event, multiple memories often become intertwined, including memories of neutral factors that were present when the event occurred. Part of this research is looking into helping people with triggering memories that have little to do with the actual traumatic event, aside from it just being there, and unlinking the trigger from the trauma.

An example is of someone who gets mugged, then sees a mailbox. Researchers said that mailbox could trigger feelings of anxiety later when someone wants to go put a letter in the mail.

"In the example, fear of dark alleys is an associative memory that provides important information—dark alleys may lead to another mugging—and is based on a previous associative experience," wrote Schacher. "Fear of mailboxes, however, is an incidental memory that is not related to the event. Selective erasure of this type of memory would be beneficial."

Despite good intentions, if we've learned anything from any movie ever about drugs that mess with the mind, there is reason to proceed with caution.

"Obviously drugs designed to help individuals with real needs can be abused, opioids designed as anesthetics or for pain relief are now being abused," wrote Schacher. "An essential role of government is regulating how drugs are tested and distributed, and making sure that medical professionals use them appropriately." The next step is to do some further research on how these memory-strengthening molecules are produced before scientists can determine which drugs can block them. Until then, we're a little ways off from Eternal Sunshine of the Spotless Mind becoming a reality.