Memories 'lost' to Alzheimer's is recoverable

What if lost memories could be switched on? A team of scientists has come up with a technique that can be used to restore thoughts that have been lost.

The MIT neuroscientists reported 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.

"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 senior author Susumu Tonegawa from RIKEN-MIT Center for Neural Circuit Genetics.

The researchers studied two different strains of mice genetically engineered to develop Alzheimer's symptoms, plus a group of healthy mice.

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

The researchers also showed that the engram cells of Alzheimer's mice had fewer dendritic spines, which are small buds that allow neurons to receive incoming signals from other neurons.

"If we want to recall a memory, the memory-holding cells have to be reactivated by the correct cue. If the spine density does not go up during learning process, then later, if you give a natural recall cue, it may not be able to reach the nucleus of the engram cells," Tonegawa says.

The researchers were also able to induce a longer-term reactivation of the "lost" memories by stimulating new connections between the entorhinal cortex and the hippocampus.

According to Tonegawa, it's possible that in the future some technology will be developed to activate or inactivate cells deep inside the brain, like the hippocampus or entorhinal cortex, with more precision. Basic research, as conducted in this study, provides information on cell populations to be targeted, which is critical for future treatments and technologies.

The study appears in Nature.