LONDON: The researchers of California say that they have made a breakthrough in restoring memories. They say the work, in snails, could one day lead to new hope for patients in the early stages of Alzheimer’s disease.
It also reveals how long term memories are stored – proving a popular theory wrong. For decades, most neuroscientists have believed that memories are stored at the synapses – the connections between brain cells, or neurons which are destroyed by Alzheimer’s disease. The new study provides evidence contradicting the idea that long-term memory is stored at synapses.
‘Long-term memory is not stored at the synapse,’ said David Glanzman, a senior author of the study, and a UCLA professor of integrative biology and physiology and of neurobiology. ‘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.’
The findings were published recently in eLife, a highly regarded open-access online science journal. Glanzman said the research could have significant implications for people with Alzheimer’s disease. Specifically, just because the disease is known to destroy synapses in the brain doesn’t mean that memories are 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,’ he said. Glanzman added that in the later stages of the disease, neurons die, which likely means that the memories cannot be recovered. Glanzman’s research team studies a type of marine snail called Aplysia to understand the animal’s learning and memory.
The Aplysia displays a defensive response to protect its gill from potential harm, and the researchers are especially interested in its withdrawal reflex and the sensory and motor neurons that produce it. They enhanced the snail’s withdrawal reflex by giving it several mild electrical shocks on its tail. The enhancement lasts for days after a series of electrical shocks, which indicates the snail’s long-term memory. Glanzman explained that the shock causes the hormone serotonin to be released in the snail’s central nervous system.
After erasing the memory, scientists repeated the experiment in the snail, and then gave the animal a modest number of tail shocks – which do not produce long-term memory in a naive snail – the memory they thought had been completely erased returned. This implies that synaptic connections that were lost were apparently restored. ‘That suggests that the memory is not in the synapses but somewhere else,’ Glanzman said. ‘We think it’s in the nucleus of the neurons. We haven’t proved that, though.’ The researchers also wanted to understand whether synapses disappeared when memories did.
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