New research suggests that memories may not be stored by synaptic connections between neurons in the brain, but rather synapses may allow the expression of memories that are stored elsewhere in the neuron.
The revolutionary study by academics at the University of California has suggested for the first time that memories are not stored in synapses as previously thought. It is synapses, the connections between brain cells, that are destroyed by Alzheimer’s.
The breakthrough, reported in the highly regarded online journal eLife, could mean that it becomes possible to restore lost memories.
“Long-term memory is not stored at the synapse,” said David Glanzman, the study’s co-author and professor of integrative biology and physiology and of neurobiology at UCLA. “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.”
Professor Glanzman’s team studied the marine snail Aplysia to understand the animal’s learning and memory functions. Glanzman was particularly interested in the Aplysia’s defensive reactions and the sensory and motor neurons responsible for its withdrawal response.
“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 Prof. Glanzman. “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.”
As part of the test, the snails were given a number of electric shocks, which in themselves would not usually produce long-term memories. The team found that the memories they thought had been completely erased earlier in the experiment had returned, suggesting that synaptic connections that had previously been lost were apparently restored.
“That suggests that the memory is not in the synapses but somewhere else,” said Glanzman. “We think it’s in the nucleus of the neurons. We haven’t proved that, though.”
He added that the research could be a major breakthrough for Alzheimer’s sufferers as even though the disease destroys synapses in the brain, memories might not necessarily destroyed.
“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,” said Prof Glanzman.