Scientists have been able to transfer a memory from one snail to another, providing a tantalising clue to the answer of one of most vexing questions in biology - how are memories stored?
"It's like we carried the memory", said Gladman and argued that memories are not stored in synapses of neurons (each neuron has several thousand synapses), as is widely believed, but in the nucleus of neurons.
In an experiment, researchers inflicted painless electric shocks to sea snails known as Aplysia californica.
Once the reflex action had been established in the trained snails, they were euthanised and their abdominal ganglia removed.
Some of the new snails received RNA from the trained cohort, and some, as controls, from the untrained group. When the snails were tapped slowly by the researchers, the snails that received a shock displayed a slight contraction that lasted for 50 seconds but the ones without any shock treatment showed contractions only for one second.
The researchers extracted RNA, which was accumulated in the nervous system of animals after the shocks, and not sensitized. The snails that didn't receive the training contracted for only a second.
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Speaking of what this means, Glanzman said: "What we are talking about are very specific kinds of memories, not the sort that says what happened to me on my fifth birthday, or who is the president of the USA". Like all mollusks, these snails have groups of neurons called ganglia, rather than brains. After the shocks, scientists took RNA from the slugs that were shocked and injected it into slugs that hadn't been shocked. The researchers also tested some of the same techniques on snail neurons in a petri dish.
The world's first memory transplant was just achieved in marine snails. But UCLA neurobiologist David Glanzman subscribes to a different theory: the key to at least some memory storage, he thinks, is RNA, the cellular "messenger" that makes proteins and transmits DNA's instructions to other parts of the cell.
He said: "If memories were stored at synapses, there is no way our experiment would have worked". Instead, his team suggests that long-term memories are actually encoded in RNA molecules, just like it happened in the case of the sea snails.
In the future, Glanzman said, it is possible that RNA can be used to awaken and restore memories that have gone dormant in the early stages of Alzheimer's disease. In fact in 2014 his team had already published a paper which implied that lost memories could be restored.
Glanzman says that in his next experiments he will attempt to identify the RNAs involved, and he has an idea for the mechanism, too.
The research was funded by the National Institute of Neurological Disorders and Stroke, the National Institute of Mental Health and the National Science Foundation.