This Medical News Today reprint illustrates the work yet to be done to determine why first generation stem cell based regenerative medicine produces results. "Our study showed that cell transplantation therapy may improve brain receptor function in patients who suffered from cerebral stroke, improving their neurological symptoms. How the transplanted bone marrow stromal cells restore the lost neurologic function is not clear." An argument could be made that the difference between therapies of the past and therapies of the future is in understanding the biochemical mechanisms involved - i.e. how it works. Early stem cell therapies straddle the line: researchers know enough to build this medical technology, but not - yet - to determine why they obtain good results.