More Science See Inside Neural Stem Cell Transplants May One Day Help Parkinson's Patients, Others Neurodegenerative disorders devastate the brain, but doctors hope one day to replace lost cells By Ferris Jabr Bryan Christie Inside the human brain, branching neurons grow beside, around and on top of one another like trees in a dense forest. Scientists used to think that any neurons that wilted and died from injury or disease were gone forever because the brain had no way to replace those cells. By the 1990s, however, most neuroscientists had accepted that the adult brain cultivates small gardens of stem cells that can turn into mature neurons. This is only a preview. Get the rest of this article now! Select an option below: Buy Digital Issue Customer Sign In *You must have purchased this issue or have a qualifying subscription to access this content It has been identified that the institution you are trying to access this article from has institutional site license access to Scientific American on nature.com. Click here to access this article in its entirety through site license access. ADVERTISEMENT Scientific American is a trademark of Scientific American, Inc., used with permission © 2015 Scientific American, a Division of Nature America, Inc. All Rights Reserved.