Nature 485, 646–650 (2012); 10.1038/nature11052

On page 3 of the PDF and print version of this Letter, column two, in the text describing the mEPSC frequency and dendritic spine density values shown in Fig. 3b and 3c, the words ‘saline’ and ‘cno’ were erroneously exchanged. The correct text should read: (D1-Cre, direct pathway MSNs: frequency, saline 0.8 ± 0.1 Hz, n = 18; cno 0.36 ± 0.07 Hz, n = 25; spine density, saline 0.96 ± 0.04 spines per μm, n = 5; cno 0.49 ± 0.05 spines per μm, n = 5; D2-Cre, indirect pathway MSNs: frequency, saline 0.04 ± 0.01 Hz, n = 7; cno, 0.27 ± 0.09 Hz, n = 8; spine density, saline 0.54 ± 0.05 spines per μm, n = 5; cno 0.98 ± 0.06 spines per μm, n = 5). This has been corrected online in the PDF and HTML of the original paper.