The stem cells help in an unexpected way. Rather than replacing dead or damaged memory cells in the brain, the stem cells release a protein that increases connections between existing neurons.
Instead of filling in the memory holes left by lesions, the stem cells are just making all the other memory cells work more effectively.
The protein being secreted, if isolated, could be produced to help people with memory loss, researchers suggest. The mice were given neural stem cells. A human would receive human neural stem cells from a human brain, perhaps from an organ donor. These are different than embryonic stem cells, about which ethical debates abound.
“We see that in [the hippocampus] there are much more connections between the remaining cells if we added our stem cells,” said Matthew Blurton-Jones, a contributing author and researcher to the study published in the Oct. 31 Journal of Neuroscience.
Scientists introduced a jellyfish protein that glows green under black lights into their genetically-engineered mice, that were created solely for their glowing stem cells. They then injected those easily traceable cells into the mice that suffered from lesions.
Only about 4%, or 8,000 of the cells, turned into memory cells, which led the scientists to conclude that the boosted connections — not the new neurons — recovered the memory.
The research team tested the mice’s place and object recognition. Mice were put in a square environment with two round objects in the middle, then a round environment with two square objects in the middle. The mice had five minutes to explore and remember their environments.
The team then switched one of the round and square objects with each other. If the mice explored (sniffed, looked at, circled) the new object more than the rest of the area, it meant they remembered everything except, of course, the new object. If they explored the whole environment again like it was new, it showed a problem with their memory.