Nat. Neurosci. 15, 1198–1200 (2012); published online 29 July 2012; corrected after print 13 May 2013

In the version of this article initially published, grant acknowledgments for the Human Frontier Science Program (J.T.A.) and the Bernstein Centre Göttingen (M.C.G.) were missing. The error has been corrected in the HTML and PDF versions of the article.