Losing your memory can be a terrible thing, but most of us have a few specific memories we would very much like to forget. Recently, neuroscientists have made progress in erasing traumatic memories, albeit only in animals with brains much smaller than ours. New research advances this, identifying the memories that can be removed, and those we might be stuck with.
The beta-blocker propranolol has been claimed to be able to remove learned trauma. Although we can't ask animals whether they feel better after being given it, scientists demonstrated as far back as 2004 that propranolol can unwind trauma-based responses in animals. Unfortunately, however, attempts to reproduce the results have produced inconsistent findings.
At the European College of Neuropsychopharmacology annual meeting in Lisbon, a team led by Dr Amy Milton of Cambridge University presented evidence for why propranolol doesn’t always work on memories. Milton reported that a molecule known as the “shank” protein preserves memories in the face of attempts to erase or modify them. Where the shank protein is degraded, propranolol can wash memories away.
“We trained rats to associate a clicker with a mild electric footshock, to create a fear memory, similar to the way Pavlov conditioned dogs more than a hundred years ago. We then reminded the rats of this memory (‘reactivated the memory’) by introducing the clicker on its own, and immediately after this reminder we gave an injection of the beta-blocker propranolol,” Milton said in a statement.
“However, we did not see the amnesia that had been previously reported in the literature following this intervention. We then used the presence of the shank protein to determine whether the memories had become unstable in the first place, and found that they had not.”
Milton added that it is not yet known whether the shank protein causes a memory to become immovable, or if it is a by-product of the fixing process. Either way, however, the protein could act as a marker for the prospects of successful removal.
“This is animal work; the brains of humans are similar, but much more complex,” Milton noted. “We don’t see this leading to the sort of situation shown in the movies, like for example Eternal Sunshine of the Spotless Mind, where the protagonists can choose which memories to erase.” Nevertheless, the fact the team is working on rats, rather than the snails that have been the subject of many memory erasure studies, indicates application to humans is getting closer. Rather than simply scrubbing embarrassing or irritating memories, Milton hopes the work could be applied to the sort of traumatic experiences that can cause serious distress.
“In ancient Greek legend they spoke of a drug, Nepenthe, which made them forget painful memories,” Milton said. “We hope that this is a step on the path to treatment”.
Other memory-erasing techniques have been developed (leaving aside highly dubious claims), whether they be changing the way we think about a memory’s context or stimulating neurons with light. Whether these approaches are similarly subject to the shank protein remains to be seen, as its relevance to the successful transfer of memories from one snail to another.