Pasko Rakic and Colin Blakemore, of Yale and Oxford universities, respectively, have identified the very first population of neurons to migrate into the developing cerebral cortex.
Here’s the abstract of the Nature Neuroscience paper:
We describe a distinctive, widespread population of neurons situated beneath the pial surface of the human embryonic forebrain even before complete closure of the neural tube. These ‘predecessor’ cells include the first neurons seen in the primordium of the cerebral cortex, before the onset of local neurogenesis. Morphological analysis, combined with the study of centrosome location, regional transcription factors and patterns of mitosis and neurogenesis, indicates that predecessor cells invade the cortical primordium by tangential migration from the subpallium. These neurons, described here for the first time, precede all other known cell types of the developing cortex.
The authors speculate that the predecessor cells provide a scaffold over which subsequent waves of newly-generated cortical neurons migrate over, and then die once the process is complete.
The discovery of predecessor cells may provide neuroscientists with a better understanding of developmental disorders, and could help evolutionary biologists figure out how the brain of our hominid ancestors expanded during the evolution of our species.