Using a clever new technique, researchers at the University of California, Irvine, have shown that stem-cell transplants may improve memory after brain injury, at least in mice. Their work adds to growing evidence that stem cells might eventually help combat the devastating memory loss associated with traumatic brain injury, Alzheimer's disease, and stroke.

"It's a nice piece of work," says Jack Price, professor of developmental neurobiology and director of the Centre for the Cellular Basis of Behaviour at King's College London, who was not involved in the research. "The challenge now is to go from those animal models into the clinic."

Mathew Blurton-Jones and his colleagues at the University of California, Irvine, genetically engineered mice so that they could trigger brain damage only in the hippocampus, a region of the brain that's important in spatial memory. They then transplanted neural stem cells into that area. Three months later, those mice performed about as well on memory tests as uninjured animals did.

"This is some of the more clear-cut evidence that you can improve memory in a mouse--specifically memory--with stem cells," says Blurton-Jones. The researchers describe their work in this week's issue of theJournal of Neuroscience

Previous research has shown that stem-cell transplants can help restore movement in animals after brain or spinal-cord injury. But the impact of stem-cell transplants on cognitive function, which in many ways is more complex than motor function, has been less clear, with different studies yielding conflicting results. Part of the problem, says Blurton-Jones, is that commonly used animal models involve extensive damage to the brain, which "made it very difficult to dissect out what's going on."

It's still not clear, though, how the transplanted stem cells help. "The question is, do they really, truly replace lost cells?" says Price.

Probably not. Blurton-Jones suspects that "the way our cells improved the memory in mice was not by replacing those dead cells but by helping to maintain those surviving cells." Several months after the stem-cell transplants, he found more synaptic connections in the hippocampus of treated mice compared with controls, as well as a slower rate of neuron death.

"Our data are suggesting that stem cells can have a beneficial effect that doesn't require them to take the place of dead cells," Blurton-Jones says. "They may be more versatile than we give them credit for."

Boosting cell survival is likely to be a key component of future stem-cell therapies, according to Arnold Kriegstein, director of the Program in Developmental and Stem Cell Biology at the University of California, San Francisco. "I doubt that we're likely to replace the cells that are dying" in diseases like Alzheimer's or after brain injury or stroke, he says. "But it may be possible to prevent them from dying."