Cover picture: The suprachiasmatic nuclei (SCNs) of the hypothalamus are the master circadian pacemakers in mammals. In Karatsoreos et al., the authors delineate two separate populations of cells in the mouse SCN: one rhythmic, and the other not rhythmic but light responsive. A large proportion of the light-responsive cells contain gastrin-releasing peptide (GRP). On the cover, the image shows the mouse SCN stained for vasopressin (red) and a green fluorescent protein tag on GRP-positive cells (green). For details, see the article by Karatsoreos in this issue (pages 68–75).