Oligodendrocytes must migrate to produce periodically spaced membrane sheaths along their target axons. Kirby and colleagues imaged oligodendritic precursors in vivo to study the mechanisms underlying this process. On the cover is an image from a time-lapse video showing oligodendrocyte progenitor cells, marked by green fluorescent protein, migrating in a zebrafish larva. (pp 1506)

Many neurons in cortical area MT are selective for the motion of complex patterns, independent of their component orientations. Rust and colleagues now propose a new model that predicts these neuronal responses based on previously described properties of neurons in primary visual cortex. The cover shows a contour map representing the responses of a pattern-selective neuron in macaque MT to the set of moving gratings and plaids shown in the background. (pp 1356 and 1421)

Developmental disorders such as dyslexia, autism and fragile X syndrome can affect a wide range of cognitive and social functions that arise in childhood. Researchers suspect that multiple genes in early development, as well as environmental factors, may influence the course of these disorders, but surprisingly little is known about their etiology. In this issue, we present several perspectives on the neurobiology of developmental disorders and their relationship to one another. This special focus is sponsored by the March of Dimes, Cure Autism Now and Autism Speaks. (p 1209)

Both apical and basal progenitor cells in the subventricular zone contribute to cortical neurogenesis, but only apical cells are self-renewing. A study by Capello and colleagues now shows that the Rho-GTPase cdc42 is critical for maintaining apical progenitors, and that its loss leads to their conversion into basal progenitors. The cover shows progenitor cells labeled by RC2 immunostaining in red attached to the basement membrane labeled by laminin immunostaining in green. (p 1099)

The origins of the neural underpinnings of language are controversial. A study by Ricardo Gilda-Costa and colleagues suggests that the neural substrate for human speech evolved from an ancestor common to humans and macaque monkeys. The authors used PET imaging in macaque monkeys to find activity specific to macaque vocalizations in monkey brain areas homologous to human perisylvian language areas. The cover shows an image of a macaque monkey, which shared a common ancestor with humans 25-30 million years ago. Photo credit: Marc Hauser. (p 1064)

Bystron and colleagues report a new population of neurons in the primordial cortex of 31-day-old human embryos. These cells, which may be the first neurons of the human cortex, are not generated from the local ventricular zone, but immigrate into the cortical domain from an unknown outside source. The cover shows one of these 'predecessor neurons', stained golden for βIII-tubulin, atop the cortical ventricular zone. All cell nuclei are labeled blue. (pp 867 and 880)

The optic nerve does not regenerate after injury in mature mammals, but retinal ganglion cells do regenerate lengthy axons beyond the site of optic nerve injury when stimulated by macrophage activation in the eye. Benowitz and colleagues now show that the Ca2+ binding protein oncomodulin is a macrophage–derived growth factor for retinal ganglion cells and other neurons. The cover image shows two injured optic nerves, the bottom one from an animal that has been treated with oncomodulin plus a cAMP stimulant, resulting in robust axon regeneration. (pp 715 and 843)

Defining the connections between various cell types in the mammalian retina remains a major challenge. Li and DeVries show that cone photoreceptors in the ground squirrel form extremely specific connections with different bipolar cell types. These connections may enhance visual acuity and motion sensitivity, and may also contribute to color opponency critical for color vision. The cover image shows the dendritic tree of a b5 bipolar cell reconstructed from serial confocal images. M- and S-cone terminals are outlined in green and blue, respectively. (pp 595 and 669)

In a Bayesian model of human motion perception, a prior expectancy for slow speeds is combined with sensory information. Low contrast stimuli provide a weaker sensory signal, so the prior contributes more to perception. Fixating on the central point of this cover image elicits a stronger illusion of motion in the surrounding circles with higher contrast. In this issue, Stocker and Simoncelli show that the prior in human speed perception can be derived from psychophysical measurements. (pp 468 and 578)

Like the similar physical appearance of the seven crabs in this image, the neuronal output of the crab stomatogastric ganglion is largely conserved across animals. In contrast, Schulz and colleagues report that the expression and conductance of ion channels mediating this output can be highly variable in neurons of the same class in different crabs. Comparisons of these conductances within and across animals and neurons also shed light on the constraints imposed on possible solutions for a given network behavior. p 356)

Increased local blood flow in response to changes in neural activity is critical for normal brain function. Takano and colleagues use an elegant new approach to study this effect in vivo, where all elements of the neurovascular unit are intact and functioning under normal physiological conditions. They show that astrocytes are important in translating neural activity into vasodilation via a mechanism involving COX1 metabolites. The cover image shows a section of cortex from a transgenic mouse expressing green fluorescent protein under an astrocyte promoter. Astrocytes are labeled white, neuronal processes are red, and nuclei are stained with a blue dye. (pp 159 and 260)

The mechanisms of axon and dendrite morphogenesis during neuronal maturation are not fully understood. Many previous studies have focused on neurites forming de novo from dissociated cells, but in this issue, Morgan and colleagues suggest a different mechanism may occur in vivo. They show that axons and dendrites of retinal bipolar cells form directly from neuroepithelial-like processes of immature bipolar cell precursors. The cover image shows a cross section through a mature mouse retina with immunolabeled photoreceptors (purple), amacrine and ganglion cells (red) and bipolar cells (green). (pp 16 and 85)