Nature Communications 7 Article number: 10833 (2016). Published 1 March 2016; Updated 14 August 2017

Technical support for this Article was not fully acknowledged. The Acknowledgements should have included the following: We thank Drs Ronald Petralia and Ya-Xian Wang, members of the Advanced Imaging Core, National Institute of Deafness and other Communication Disorders (NIDCD), for the images in Fig. 1k, l.