Under the right conditions, these cells can replenish themselves indefinitely in the laboratory, and they can, in theory, turn into any type of cell in the body.
Embryonic stem cells are seen by many researchers as having great potential because they can in theory be coaxed to create any kind of cell type in the body.
Evidence to bolster this theory comes from research showing that existing depression treatments all seem to spur brain cell production--just not as efficiently as we'd like.