Let there be light: Lost memories restored to Alzheimer's mice - CNET

In the case of the Alzheimer's mice, these dendritic spines dwindled as the disease progressed. Through the use of fibre-optic light stimulation, the team was able to regrow these spines, and the mice's memories were restored.

In particular, the team subjected both the Alzheimer's mice and a control group of mice to a chamber where they received a small shock. An hour later, both groups of mice reacted with fear to the chamber. However, several days later, only the non-Alzheimer's control group reacted with fear, indicating that the Alzheimer's mice had forgotten the chamber.

The team used viruses to tag the brain cells active when the mice were frightened, allowing the researchers to visually identify the neurons that were involved in the memory. A second virus made those neurons sensitive to light. When the team reactivated those cells with light, the Alzheimer's mice showed fear.

"Directly activating the cells that we believe are holding the memory gets them to retrieve it," said lead author Dheeraj Roy. "This suggests that it is indeed an access problem to the information, not that they're unable to lea or store this memory.

However, memories activated with this method faded within a day. It was then that the team linked the fading memories to the loss of dendritic spines.