There may yet be hope for Alzheimer's patients everywhere, as new research indicates that lost memories can be regained.
Neuroscientists have long believed that memories are stored at the synapses - the connections between neurons - that are destroyed by Alzheimer's disease. Long-term memories are formed by the brain which creates new proteins involved in making new synapses.
But a team from the University of California, Los Angeles (UCLA) is turning the tables on this previous notion, saying that synapses could be reactivated by a "reminder" stimulus involving memory within the neurons themselves.
"Long-term memory is not stored at the synapse," David Glanzman, a UCLA professor and senior author of the study, said in a statement. "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."
To gain a better understanding of Alzheimer's effect on memory, Glanzman and his colleagues studied a sea slug known as Aplysia. Specifically, they focused on the snail's defense response and the sensory and motor neurons involved.
The researchers enhanced its withdrawal reflex by mildly shocking the snail on its tail, with the response lasting for days afterwards.
"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."
Although it may seem difficult to apply the memory of simple sea snails - which possess a mere 20,000 neurons compared to the trillions of neurons that humans have - Glanzman says the study is worth pursuing as it could have significant implications for people suffering from the early stages of Alzheimer's disease.
"As long as the neurons are still alive, the memory will still be there, which means you may be able to recover some of the lost memories in the early stages of Alzheimer's," he suggests.
However, in the later stages of Alzheimer's it's the neurons themselves that die, meaning memories probably can't be recovered, he acknowledges.
The findings are described further in the journal eLife.
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