Correction to: Nature Neuroscience https://doi.org/10.1038/s41593-018-0073-9, published online 5 February 2018.
In the version of this article initially published, the traces in Fig. 1j and in Fig. 1k, right, were duplicated from the corresponding traces in Fig. 1c, bottom, and Fig. 1d, bottom right. The error has been corrected in the HTML and PDF versions of the article.