Investigators from the Yale School of Medicine and the University of Oxford have identified what they believe are the very first neurons of the developing cerebral cortex:
The findings published in Nature Neuroscience show that the first neurons, or “predecessors,” as the researchers called them, are in place 31 days after fertilization. This is much earlier than previously thought and well before development of arms, legs or eyes.
“These neurons, described here for the first time, precede all other known cell types of the developing cortex,” the researchers said in their paper. “These precocious predecessor neurons might be important in the cascade of developmental events leading to the formation of the human cerebral cortex…”
“We hypothesize that these predecessor neurons may be a transient population involved in determining the number of functional radial units including the human specific regions of the cerebral cortex mediating higher cognitive functions,” Rakic said. [Pasko Rakic is a chairperson of the Department of Neurobiology at Yale –ed.] “As a next step it is essential to determine their neural stem cell lineage, pattern of gene expression, developmental role and eventual fate.”
Pinpointing the early development of the cerebral cortex may help in understanding the many developmental disorders of higher brain function, such as autism, schizophrenia, childhood epilepsy, developmental dyslexia and mental retardation. It also may explain how the human brain developed differently from that of other species.
Until recently it was thought that cortical neurons were generated locally, but this research team describes a distinctive, widespread population of neurons situated beneath the surface of the human embryonic forebrain even before complete closure of the neural tube.
Predecessor cells, unlike mature nerve cells, do not have synaptic connection with other neurons. They do have long processes, or “tails,” with one stretching out in front of the cell body and the other trailing behind. Analysis of the skeleton of these cells suggests that they migrate upwards in the surface of the developing brain and enter the future cortex.
The researchers found that the processes form a vast network and they speculate that this web of processes might be used to control neuronal production, guide the migration of cells and determine the regional specification of the cerebral cortex.