Mutations in the doublecortin gene cause cortical malformations ('double cortex') in humans, but oddly, mice deficient for the gene appear normal. Joseph LoTurco and colleagues now use RNA interference to reduce doublecortin levels in rats and mice and report a disruption of radial migration, with cells stopping prematurely below or within incorrect layers of the developing neocortex. In addition to verifying the importance of DCX function during cortical development, the study also sends a cautionary message about conclusions drawn from gene knockout approaches. (pp 1245 and 1277)

The morphologically complex dendritic trees of mammalian central neurons are a critical component of neural circuits. In this issue, Yu and Malenka report that β-catenin regulates dendritic arborization in rat hippocampal neurons. Moreover, activity-induced dendritic growth requires β-catenin and Wnt release. The authors conclude that intracellular levels of the cadherin/catenin complex may be a limiting factor for dendritic morphogenesis. (p 1169)

Regulation of the timing of sleep based on circadian rhythms and regulation of the need for sleep based on sleep debt have been considered separate mechanisms. Johanna Meijer and colleagues now show in rats that sleep state influences neuronal activity in the suprachiasmatic nucleus, the main circadian pacemaker, suggesting that these processes are functionally linked. See pages 1005 and 1122.

In this issue, Micheva and colleagues show that postsynaptic activity, through the retrograde action of nitric oxide, regulates presynaptic vesicle recycling. In cultured hippocampal neurons, the colored spots represent synapses loaded with an FM dye. Blue represents slower rates of dye unloading and pink the fastest. (pp 905 and 925)

How do partial agonists elicit partial responses? Now, Eric Gouaux and colleagues combine crystallography with electrophysiology to study this question in the AMPA type of glutamate receptor. They find that partial agonists induce distinct conformational states of the ligand-binding core, thus changing the open probability of discrete subconductance states of the channel. (pp 788 and 803)

Music is a universal feature across all human societies, both ancient and modern. Yet the 'biological' function of music remains largely mysterious and much debated. Research on how the brain processes music is interesting in its own right, but it is also beginning to have an impact on more general questions in neuroscience, such as how genes and the environment interact to produce distinct cognitive abilities and how complex motor sequences are organized and learned. This month's special focus highlights this emerging research. (pp 661–695). Cover image: "Musicians and Dancers Performing" by Coco Masuda.

Eight photoreceptor neurons make up each individual ommatidium in the fly eye. Axons from these neurons target specific sites, called 'cartridges', in the brain. Zipursky and colleagues now report that flies with a non-functional mutant form of the cadherin-related cell surface protein Flamingo show disrupted patterning of photoreceptor axons to their targets. See page 557.

Experience-dependent changes in postsynaptic structure are well known, but Pico Caroni and colleagues now show that mature presynaptic terminals are dynamic structures as well. Using targeted GFP expression, they examined mossy fiber presynaptic terminals in mouse hippocampal slices. Terminals appeared and disappeared within 1-3 days and showed distinct properties based on terminal type. High-frequency stimulation increased the fraction of dynamic terminals via AMPA receptors, PKA and protein synthesis. See page 491.

The hormone oxytocin is important for labor and lactation in mammals, and giving birth was known to improve spatial memory in rats. Tomizawa and colleagues now report that intra-cerebroventricular injections of oxytocin improve spatial memory in mice that have never been pregnant, while an oxytocin antagonist inhibits the memory improvement normally seen in mice with multiple litters. Oxytocin also facilitates long-lasting, long-term potentiation in hippocampal slices. The authors suggest that oxytocin-associated memory improvement could help mothers remember the location of food sources and thus improve the survival of their young. Photograph courtesy of PhotoResearchers. See pages 327 and 153.

Which column comes next in the series? Such questions are often used in measures of general intelligence. Jeremy Gray and colleagues report that individuals who score high on a test of general fluid intelligence also show increased fMRI activity in brain areas involved in attention, including the lateral prefrontal cortex. This correlation was apparent only when participants were performing a demanding memory task. Therefore, individual differences in general intelligence might depend in part on differences in neural systems involved in the control of attention. (The correct answer is A.) See pages 207 and 316.

The EphA4 ephrin receptor (labeled in red) is enriched on dendritic spines of pyramidal neurons in the adult mouse hippocampus. Its ligand, ephrin-A3, is localized to adjacent astrocytes. Pasquale et al. show that neuroglial cross-talk via this ligand-receptor signaling system can regulate spine morphology. The authors used mice expressing yellow fluorescent protein (green) in a subset of neurons to monitor spine morphology. See pages 103 and 153.

We can often predict the location of an object that has been occluded by another object based on its initial speed and trajectory. Barborica and Ferrera found that neurons in the frontal eye field of monkeys trained to predict the location of an invisible moving target were active even when the object was no longer in view. This activity was tuned to the speed of the moving stimulus, suggesting that information about motion itself is stored while the stimulus is occluded. Photo courtesy of Corbis. See pages 11 and 66.