Lost memories may not be gone forever, a finding that may offer hope for people suffering early-stage Alzheimer's disease, UCLA researchers say.
Most neuroscientists have held that the brain stores memories in the connections between neurons -- the synapses -- which are exactly the connections destroyed in Alzheimer's disease.
However, the UCLA study has produced evidence contradicting that long-held assumption, university researchers say.
"Long-term memory is not stored at the synapse," says David Glanzman, one of the authors of the study. "That's a radical idea, but that's where the evidence leads."
The researchers say their studies suggest "memory traces" are not stored in the synapses but instead the neuron itself has a memory of how many synapses it ought to be creating with other neurons, with the synapses just being an expression of this memory.
If that's so, they propose, then even though Alzheimer's destroys synapses the memories may not be destroyed, and it's possible they could be reactivated -- recovered -- by a "reminder" stimulus involving memory within the neurons themselves.
"The nervous system appears to be able to regenerate lost synaptic connections," says Glanzman, a professor of integrative biology and physiology and of neurobiology. "If you can restore the synaptic connections, the memory will come back. It won't be easy, but I believe it's possible."
In their study, the UCLA researchers used neurons taken from a sea slug known as Aplysia, whose simple nervous system possessing a mere 20,000 neurons or so makes it a favorite subject of neuroscientists studying memory and learning.
While the minimalist nature of the sea slug's nervous system suggests the research findings might be difficult to apply to higher forms of life, such as monkey or mice -- or humans, who have trillions of neurons creating synapses -- Glanzman says the study is worth pursuing as it could have significant implications for people suffering from Alzheimer's disease.
Just because the disease destroys synapses in the brain doesn't mean that memories are destroyed, if "the memory is not in the synapses but somewhere else," he says. "We think it's in the nucleus of the neurons. We haven't proved that, though."
"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.
