The MIT neuroscientists report in Nature that mice in the early stages of Alzheimer’s can form new memories just as well as normal mice but cannot recall them a few days later.
Furthermore, the researchers were able to artificially stimulate those memories using a technique known as optogenetics, suggesting that those memories can still be retrieved with a little help. Although optogenetics cannot currently be used in humans, the findings raise the possibility of developing future treatments that might reverse some of the memory loss seen in early-stage Alzheimer’s, the researchers say.
Normally, when a new memory is generated, the engram cells corresponding to that memory grow new dendritic spines, but this did not happen in the Alzheimer’s mice. This suggests that the engram cells are not receiving sensory input from another part of the brain called the entorhinal cortex. The natural cue that should reactivate the memory — being in the chamber again — has no effect because the sensory information doesn’t get into the engram cells.
“The important point is, this a proof of concept. That is, even if a memory seems to be gone, it is still there. It’s a matter of how to retrieve it,” says Susumu Tonegawa, the Picower Professor of Biology and Neuroscience and director of the RIKEN-MIT Center for Neural Circuit Genetics at the Picower Institute for Learning and Memory.
“This is a remarkable study providing the first proof that the earliest memory deficit in Alzheimer’s involves retrieval of consolidated information,” says Rudolph Tanzi, a professor of neurology at Harvard Medical School, who was not involved in the research. “As a result, the implications for treatment of memory deficits Alzheimer’s disease based on strengthening synapses are extremely exciting.”