New research has shown that contrary to popular belief, memories might not actually be stored in the synapses of neurons, which could have some pretty remarkable implications.
The study led by David Glanzman of UCLA, which was published in eLife, involved looking at marine snails known as Aplysia, and the results show that the memory-synapses link isn’t what we thought it was. The reason this is such a big discovery is because if synapses destruction isn’t the reason for memory loss, there might be potential for memory restoration for patients with early onset Alzheimer’s.
“Long-term memory is not stored at the synapse,” Glanzman said in a press release. “That’s a radical idea, but that’s where the evidence leads. The nervous system appears to be able to regenerate lost synaptic connections. If you can restore the synaptic connections, the memory will come back. It won’t be easy, but I believe it’s possible.”
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In order test the snail’s memory, they needed to trigger its defense response. Aplysia have delicate gills, which they are very quick to shield from damage. This reflex was bolstered by administering small electrical shocks on the tail. The snails began to form short-term memories associated with the shock due to the release of the neurotransmitter serotonin. Over time, the serotonin and secreted proteins creates synaptic connections associated with the formation of long-term memories. Injuries (like concussions) or other factors can interrupt this from occurring normally, which prevents the formation of long-term memories. For this study, the researchers artificially interrupted the progress to explore the creation and preservation of long term memories.
“If you train an animal on a task, inhibit its ability to produce proteins immediately after training, and then test it 24 hours later, the animal doesn’t remember the training,” Glanzman explained. “However, if you train an animal, wait 24 hours, and then inject a protein synthesis inhibitor in its brain, the animal shows perfectly good memory 24 hours later. In other words, once memories are formed, if you temporarily disrupt protein synthesis, it doesn’t affect long-term memory. That’s true in the Aplysia and in human’s brains.”
Sensory and motor neurons that were associated with long-term memories we removed from the snails. Later, serotonin and certain proteins were introduced to the neurons in the same dish which ended up actually creating new synaptic connections just like what would happen in the live snail.
This seems to indicate that though synaptic connections are associated with long-term memory, that is not where they are stored. Otherwise, the connections would not have been able to re-form where they did. However, they aren’t sure where exactly they are stored. Glanzman said his team suspects that memories are stored in the nucleus of the neurons, but they are currently not able to prove that.
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