Cover Picture: The magnetic resonance image on the left is an axial view of the brain of a premature human infant born at 26 weeks gestational age. The background of the image is a map of the brain water apparent diffusion coefficient. Regions of white matter appear brighter than grey matter because water inthe former has a higher apparent diffusion coefficient than that in the latter at this stage of development. The yellow lines superimposed on the image show the direction in which water diffusion is highest for each brain region. In the cortex, diffusion is highest in a radial direction. This is particularly conspicuous in the magnified view of the frontal cortex (inset). The image on the right is a silver stain by Cajal from the precentral gyrus of a 1-month-old child (reproduced with permission, Cajal Institute, CSIC, Madrid, Spain; copyright inheritors of Santiago Ramón y Cajal). Note the radial orientation of the apical dendrites of thepyramidal cells. This organization, along with that of the radial glia, tends to restrict longitudinal water motion relative toradial motion. This is the likely explanation for the preferred radial direction of water diffusion in developing cortex. See McKinstry et al., pp. 1237-1243.
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