The anatomical and functional architecture of the human brain is mainly determined by prenatal transcriptional processes. We describe an anatomically comprehensive atlas of the mid-gestational human brain, including de novo reference atlases, in situ hybridization, ultra-high-resolution magnetic resonance imaging (MRI) and microarray analysis on highly discrete laser-microdissected brain regions. In developing cerebral cortex, transcriptional differences are found between different proliferative and post-mitotic layers, wherein laminar signatures reflect cellular composition and developmental processes. Cytoarchitectural differences between human and mouse have molecular correlates, including species differences in gene expression in subplate, although surprisingly we find minimal differences between the inner and outer subventricular zones even though the outer zone is expanded in humans. Both germinal and post-mitotic cortical layers exhibit fronto-temporal gradients, with particular enrichment in the frontal lobe. Finally, many neurodevelopmental disorder and human-evolution-related genes show patterned expression, potentially underlying unique features of human cortical formation. These data provide a rich, freely-accessible resource for understanding human brain development. A spatially resolved transcriptional atlas of the mid-gestational developing human brain has been created using laser-capture microdissection and microarray technology, providing a comprehensive reference resource which also enables new hypotheses about the nature of human brain evolution and the origins of neurodevelopmental disorders. With President Barack Obama's BRAIN (Brain Research through Advancing Innovative Neurotechnologies) initiative now entering year two, this issue of Nature presents two landmark papers that mobilize 'big science' resources to the cause. Hongkui Zeng and colleagues present the first brain-wide, mesoscale connectome for a mammalian species — the laboratory mouse — based on cell-type-specific tracing of axonal projections. The wiring diagram of a complete nervous system has long been available for a small roundworm, but neuronal connectivity data for larger animals has been patchy until now. The new three-dimensional Allen Mouse Brain Connectivity Atlas is a whole-brain connectivity matrix that will provide insights into how brain regions communicate. Much of the data generated in this project will be of relevance to investigations of neural networks in humans and should help to further our understanding of human brain connectivity and its involvement in brain disorders. In a separate report Ed Lein and colleagues present a transcriptional atlas of the mid-gestational human brain at high spatial resolution, based on laser microdissection and DNA microarray technology. The structure and function of the human brain is largely determined by prenatal transcriptional processes that initiate gene expression, but our understanding of the developing brain has been limited. The new data set reveals transcriptional signatures for developmental processes associated with the massive expansion of neocortex during human evolution, and suggests new cortical germinal zones or postmitotic neurons as sites of dynamic expression for many genes associated with neurological or psychiatric disorders.
