People with early stages of Alzheimer's disease still have their memories, they just can't access them, according to new findings published in the journal Nature.
Neuroscientists from the Massachusetts Institute of Technology found mice bred to show early signs of Alzheimer's can form new memories but can't recall them a few days later. But even though the mice cannot recall their recent experiences when prompted by natural cues, those memories are still there.
"The important point is, this is a proof of concept," says Susumu Tonegawa, senior study author, Picower professor of biology and neuroscience, director of the RIKEN-MIT Center for Neural Circuit Genetics at the Picower Institute for Learning and Memory in a university-issued news release. "That is, even if a memory seems to be gone, it is still there. It's a matter of how to retrieve it."
Researchers exposed all the mice to a chamber where they received a foot shock. They all showed fear when placed in the same chamber an hour later, but several days later, only the normal (control) mice showed fear.
Researchers then tagged the engram cells associated with a fearful experience with a light-sensitive protein. When those engram cells were activated, both the normal and Alzheimer's mice recalled the experience. Researchers reactivated the "lost" memories by stimulating connections that weren’t--but should have been--happening, suggesting a breakdown in sensory input.
The researchers were able to help mice retrieve "lost" memories through an artificial electrical stimulation technique called optogenetics. The technique is more targeted than existing methods for deep brain stimulation, sometimes used to treat Parkinson's disease, but is too invasive to be used in humans. Optogenetics does offer potential for the development of future treatments that could reverse some memory loss in early stages of Alzheimer's.