Cover legend: Retroviral injections label control neurons (green) and neurons lacking the autism-associated gene Pten (red) in the mouse dentate gyrus. Neuronal reconstructions and images of dendritic spines with labeled synapses demonstrate that Pten knockout increases cell size and synapse number, resulting in neuronal hyperactivity. Parallel morphological and physiological analyses underscore the tight coupling of neuronal structure to function. For more information, see the article by Williams et al. (pages 943–959).