In the developing embryo, nerve cells are formed from stem or progenitor cells. Scientists speculate that new nerve cells are created from these stem cells. To date, studies in adult rodents and monkeys including Gage's study in humans have found new nerve cell creation in one brain region, the hippocampus-a region involved in memory. Recently it was demonstrated that new nerve cells can be created in other brain regions. Although it's now accepted that the adult human brain is capable of creating new nerve cells, the rate of formation is low.
Environmental factors influence the rate of nerve cell creation.
If mice are placed in an enriched environment nerve cell formation increases. By contrast during stress nerve cell formation increases. They offer hope that lost nerve cells can be replaced. Perhaps by stimulating the process of nerve cell creation. They open the possibility that PD is not caused by an abnormal loss of nerve cells, but by an inability to replace lost nerve cells.