Researchers have been able to reawaken memories thought lost in mice suffering from a condition similar to Alzheimer’s disease. The technique allowed researchers to reactivate areas of the brain where memories are stored, suggesting that Alzheimer’s doesn’t cause memories to be forgotten, it simply stops the person's ability to access them.
The study, published in Hippocampus, focused on two groups of mice with genetically engineered brain cells that glow yellow when a new memory is registered and red when the same memory is accessed. One group was also engineered to develop a condition similar to Alzheimer’s, while the other acted as a control.
Both groups of mice were then given a memory test. Researchers made the mice smell a lemon scent and then gave them an electric shock. A week later, the mice were exposed to the scent again. The healthy mice froze instantaneously, expecting to be shocked, while in the Alzheimer’s group this was seen less than half as often. This implied that they had forgotten the link between the smell and the shock.
The way the two groups of mice behaved was in agreement with observations of their hippocampi, the region of the brain that records new memories. For the healthy mice, the analysis shows that the yellow-glowing cells overlapped with the red-glowing cells. This didn’t happen in the mice afflicted with Alzheimer’s. The red-glowing cells were in a different location, suggesting the mice might be accessing false memories.
The research team, led by Professor Christine Denny, wondered if the memories were gone or just inaccessible. To test this, they decided to stimulate the yellow cells with laser light, a technique known as optogenetics. The team used fiber optics to precisely target the correct cells. This was enough to get an answer. The Alzheimer’s mice were once again freezing in anticipation when they smelled lemons.
While the research is important, it isn't a cure for the condition. Optogenetics can’t be translated to a human-friendly approach – at least not yet. However, knowing that the memories might not be lost could provide novel ways to approach how the condition is managed.
Currently, research suggests that Alzheimer’s is caused by the accumulation of proteins called amyloid plaques and tau tangles in the brain. It’s a progressive disease and the most common cause of dementia. Almost 50 million people suffer from the condition worldwide.