Cover legend: An artistic rendition of a glomerulus in the mammalian olfactory bulb, with affiliated excitatory mitral cells (dark green) and external tufted (ET) cells (white) and inhibitory periglomerular (PG) cells (brown, pink, orange). Local dendrodendritic processing involving ET and PG cells appears to control whether the mitral cell output of a glomerulus is entirely ‘on’ or ‘off.’ Artwork by Greg Dunn, Neuroscience Graduate Program, University of Pennsylvania. For more information, see the article by Gire and Schoppa in this issue (pages 13454–13464).