Snail Reveals Lost Memories May be Restored: New Implications for Alzheimer's

There could be a breakthrough for Alzheimer's patients. Scientists have taken a closer look at a certain marine snail to learn a bit more about memory, and have found that it may be possible to restore "lost" memories.

In the past, neuroscientists believed that memories were stored in the synapses, which are the connections between brain cells, or neurons. Synapses are often destroyed by Alzheimer's disease. Yet in this case, the researchers found that memory may actually not be stored in these areas.

In order to learn a bit more about memory, the researchers examined a type of marine snail called Aplysia. The Aplysia displays a defensive response to protect its gill from potential harm and, in this case, the scientists were interested in this withdrawal reflex and the sensory and motor neurons that produce it.

The researchers enhanced the snail's reflex by giving it several mild electrical shocks on its tail. The enhancement lasted for days after the shocks, which indicated that the snail was using its long-term memory.

Long-term memory is a function of the growth of new synaptic connections caused by serotonin. As long-term memories are formed, the brain creates new proteins that are involved in making new synapses. If that process is disrupted, then the proteins may not be synthesized and long-term memories cannot form.

"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," said David Glanzman, one of the researchers, in a news release. "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."

The researchers also checked to see whether synapses disappeared when memories did. If the prevailing wisdom were true--memories are stored in the synapses--then the lost synapses should be the same ones that had grown in response to serotonin. The scientists found, though, that some of the new synapses were present and some were gone, and some of the original ones were gone too. This implies that memory is not stored in the synapses, which means that it may be possible to restore memories.

The findings may have implications for Alzheimer's disease research. More specifically, it could allow scientists to develop targeted treatments in the future.

The findings are published in the journal eLife.

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