This image shows hippocampal neurons stained for the neuronal marker NeuN (blue), the interneuron protein parvalbumin (green), and the neuregulin receptor ErbB4 kinase (red). ErbB4 kinase regulates the production of sharp-wave ripple events that are involved in spatial working memory. For more information, see the article by Robinson et al. (pages 390–404). Cover image: Dr. Thiri Lin (University of North Carolina).