Nat. Neurosci. 12, 1559–1566 (2009); published online 8 November 2009; corrected after print 3 December 2009

In the version of this article initially published, on page 2, left column, the phrase “...and typically cluster in glucocorticoid-rich regions called CpG islands (CGIs)” should be “...and typically cluster in GC-rich regions called CpG islands (CGIs)”. The error has been corrected in the HTML and PDF versions of the article.