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Neurosci. 3:49. doi: 10.3389/neuro.22.001.2009 This article was submitted to Frontiers in Neurogenesis, a specialty of Frontiers in Neuroscience. Copyright © 2009 Babu, Ramirez- Rodriguez, Fabel, Bischofberger and Kempermann. This is an open-access arti- cle subject to an exclusive license agreement between the authors and the Frontiers Research Foundation, which permits unre- stricted use, distribution, and reproduc- tion in any medium, provided the original authors and source are credited. www.frontiersin.org September 2009 | Volume 3 | Article 49 | 11