A new study by researchers at the Columbia University could be a catalyst in the shift of our understanding of Alzheimer’s.
The scientists have been able to reawaken forgotten memories in mice with Alzheimer’s disease, suggesting that the condition may not actually destroy our memories, but instead impair our ability to recall them.
It is believed that Alzheimer’s disease completely erases memories. The condition involves clumps of proteins known as amyloid plaques and tau tangles accumulating in the brain, where they are thought to destroy the neurons that store our memories. But experiments by Christine Denny at Columbia University and her colleagues suggest that memories may not be wiped by Alzheimer’s disease, but instead become harder to access.
What’s more, the scientists have found that these memories can be reawakened by artificially activating the neurons they are stored in.
In the course of the study, researchers examined two types of genetically engineered mice–the first one healthy and the other one with a condition similar to Alzheimer’s disease of humans. All had their neurons glow either yellow (when memory stage is activated) or red (for memory recall) to enable the researchers to have a visual representation of what’s happening inside their brain.
Later, the two
groups were subjected to a memory test- both groups were exposed to a lemon scent while being electrically shocked. When exposed to the same lemon scent a week after, the healthy mice reacted as if it’s anticipating the shock again. However, those mice with the condition reacted almost half as much as the healthy mice did. This implied that they had forgotten the link between the smell and the shock.This behaviour matched what the team saw in the hippocampi of the mice. In healthy mice, the red and yellow neurons overlapped, showing that the mice were retrieving the lemon-shock memory from the same place it had been stored. But in the Alzheimer’s mice, different cells glowed red during recall, suggesting that they were calling up the wrong memories.
Using a genetic engineering technique called optogenetics, Denny’s team went on to reactivate the lemon-shock memory in the Alzheimer’s mice. By shining a blue laser down a fibre optic cable into the brain, they were able to stimulate the yellow memory-storing neurons, prompting the mice to freeze when they smelled the lemon scent.
This shows that people with Alzheimer’s might not have actually had their memories wiped out or destroyed. Instead, the disease causes impairment that makes the recall of the memory harder.
Optogenetics is not a technique that can be used in people yet, because it isn’t yet safe or practical to tinker with our neurons or stick lasers in our brains. But in the future, targeted drugs or techniques like deep-brain stimulation may help people with Alzheimer’s access their forgotten memories, says Denny.
The finding could be revolutionary, says Ralph Martins at Edith Cowan University in Australia. “It has the potential to lead to novel drug development to help with regaining memories,” he says.
The next step will be to confirm that the same memory storage and retrieval mechanisms exist in people with Alzheimer’s disease, because mouse models do not perfectly reflect the condition in humans, says Martins. In particular, the number of neurons that die in mouse models of Alzheimer’s disease is far lower than in humans, he says.
