Nat. Neurosci. 14, 1209–1216 (2011); published online 21 August 2011; corrected after print 22 September 2011

In the version of this article initially published, the colored circles and horizontal bars above the x axis in the top panels of Figure 8, which indicate the median and central 90% range of each distribution, were misaligned. The error has been corrected in the HTML and PDF versions of the article.