Nat. Neurosci. 18, 1200–1201 (2015); published online 26 August 2015; corrected after print 22 September 2015

In the version of this article initially published, page ranges were missing for refs. 2 and 3 and the journal abbreviation was missing for ref. 21. They are, respectively, pp 1202–1212, pp 1213–1225 and Elife. The error has been corrected in the HTML and PDF versions of the article.