Researchers at Johns Hopkins, writing in the journal Cell, have found that a single brain stem cell can produce two stem cells just like itself. "If we can somehow cash in on this newly discovered property of stem cells in the brain, and find ways to intervene so they divide more, then we might actually increase their numbers instead of losing them over time, which is what normally happens, perhaps due to aging or diseases," Johns Hopkins researcher Hongjun Song said in a release. So, yes, someday your long lost brain cells could be replaced, and then some. Release | Abstract