Cover picture: A three-dimensional confocal image from rat parietal cortex layer V. Nuclei are in green (Sytox). The image was taken from an animal that was given two identical behavioral exploration sessions separated by 60 min before being killed. The image shows combined immunohistochemistry and in situ hybridization staining for Arc protein and Arc mRNA, respectively. Arc protein (in blue) was induced by the first exploration session, and Arc mRNA (in red or in pink when colocalized with the protein) was induced by the second exploration session. Note the high colocalization of Arc mRNA and its protein, suggesting that the same neural ensemble was (25X magnification). For details, see the article by Ramirez-Amaya et al. in the February 16, 2005 issue (pages 1761–1768).