Health 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 THIS IS A PREVIEW. Buy this digital issue or subscribe to access the full article. Already a subscriber or purchased this issue? Sign In 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. Researchers are still trying to determine exactly how often these stem cells become new neurons and how well these differentiated cells survive and join established brain circuits. Some evidence suggests that the brain's neural stem cells help the organ heal itself in modest ways—helping to replace small populations of neurons that suffocated during a stroke, for example. But this minimal self-repair does not restore the millions of neurons lost to stroke, traumatic brain injury and neurodegenerative diseases such as Alzheimer's and Parkinson's. THIS IS A PREVIEW. Buy this digital issue or subscribe to access the full article. Already a subscriber or purchased this issue? Sign In Buy Digital Issue $5.99 Add To Cart Digital Issue + Subscription $39.99 Subscribe 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.