CAMBRIDGE, Mass., March 17 (UPI) -- In experiments with mice that have early-stage Alzheimer's disease, scientists at the Massachusetts Institute of Technology found memories are still stored in the brain but the condition prevents them from being accessed.
The scientists used a optogenetics, a technique that involves activating brain cells with light, in a proof-of-concept study showing missing memories may still exist in Alzheimer's patients' brains -- but scientists need a method to unlock them.
Researchers at MIT have previously identified cells in the brain that store specific memories, as well as how to manipulate the cells, called engrams, to plant false memories, activate existing memories or alter emotions linked to a memory.
The researchers have also found mice with retrograde amnesia had impaired recall, but their brains continued to form new memories, causing them to question whether memories in Alzheimer's patients really disappear.
Optogenetics -- a technique causing genetically-modified cells to express light-sensitive ion channels, allowing for a certain measure of control -- is thought to be too invasive for humans, and other methods of electrically stimulating the brain, such as deep brain stimulation, affect too many parts of the brain at once.
While the method has a little chance of working for people, the researchers said understanding that memories do not disappear in those who have the disease offers promise for better treatments.
"The important point is, this a proof of concept," said Dr. Susumu Tonegawa, director of the RIKEN-MIT Center for Neural Circuit Genetics, said in a press release. "That is, even if a memory seems to be gone, it is still there. It's a matter of how to retrieve it."
For the study, published in the journal Nature, the scientists studied three groups of mice, two types that were both engineered to develop Alzheimer's disease, and a healthy group of mice.
All three groups of mice were put in a chamber and shocked on the foot. All the mice were fearful when placed in the same chamber an hour later. The next day, the Alzheimer's mice appeared to forget the shock while the healthy mice were afraid of their location.
To test whether a memory had been stored in the brain long-term, despite only being recalled in a shorter time frame -- Alzheimer's mice remembered the shock an hour later, but forgot it the next day -- the scientists tagged engram cells associated with the chamber experience to be activated by light. The scientists then put these mice in a chamber they'd never seen before and activated the engram cells, causing the mice to be afraid of an impending foot shock.
The scientists also tested whether a period of treatment using optogenetics could cause the mice to remember things on their own. The mice were given three hours of optogenetics to stimulate the proper cells in their brains, and put in the original chamber a week later. Without the prompting of scientists, the mice remembered the fear caused by getting shocked in the chamber.
"The big message is that there is a way to strengthen these memory cells," Dheeraj Roy, a doctoral student at MIT and lead author on the study, told the Boston Herald. "If we had a way of restoring the memory of patients, we think this could have a huge impact on society."