Nat. Methods 12, 64–70 (2015); published online 24 November 2014; corrected after print 11 June 2015

In the version of this article initially published, GenBank/EMBL/DDBJ accession codes for R-GECO2L and R-CaMP2 were omitted. These accession codes are KR149061 and KR149062, respectively. The error has been corrected in the HTML and PDF versions of the article.