An injury may be like a period of bad weather or people tramping over the same spot repeatedly. As these cells mature, they apparently develop into more specialized stem cells, such as those that become bone marrow, which in turn beget blood cells. We just don't know how it happens. Since the 1980s, Snyder and a small group of other researchers around the world have experimented with stem cells that give rise to various brain cells in mice. Their experiments raised the question of whether humans have the same type of cells and if these cells can regenerate a human brain the way they do in rodents.
Ongoing research suggests that they can.
The cells came mainly from an area in the center of the brain where the nervous system first starts to form. The scientists were able to grow these cells, freeze then thaw them, and transplant them into mice. They showed that these cells could grow into any of the three major types of brain cells and do so in different regions throughout the brain. If we can continue the expansion indefinitely, and if the cells can be grafted into humans, that could eliminate the need for cells from aborted fetuses, or from excess embryos discarded by fertility clinics. When transplanted into the brains of newborn mice, these cells migrated to various regions, following the same routes that cells take during normal development of a mouse brain.