Nat. Neurosci. 15, 1683–1690 (2012); published online 11 November 2012; corrected after print 11 January 2013

In the version of this article initially published, in the equation for Aθ on p. 5, the subscript to the variable f was given as an e. The correct character is θ. The error has been corrected in the HTML and PDF versions of the article.