The process by which neurons are born and migrate to the cortex is of fundamental importance to a wide range of neurodevelopmental disorders including birth defects, schizophrenia, epilepsy, and learning disabilities. We are using electrophysiological, optical recording, and molecular biological approaches to study intercellular signaling and proliferation in the embryonic cerebral cortex during fetal stages of development. Findings from our laboratory reveal that embryonic neuronal stem cells appear to be highly interactive, communicating with each other directly through gap junction channels and responding to their local environment through specific neurotransmitter receptors. In addition, we recently demonstrated that radial glial cells, present only in the embryonic and fetal developing brain and long thought to simply guide embryonic nerve cells during migration, are neuronal stem cells in the developing brain. We found that radial glial cells divide to produce nerve cells that often climb along their parent radial glial cells to reach the developing cerebral cortex. This finding suggests that a radial glial 'mother' cell generates and guides daughter neurons. More recently, we have found a second nerve cell precursor in the embryonic brain that undergoes a different mode of cell division in a distinct proliferative zone. This suggests new mechanisms for the generation of cell diversity in the developing cortex. The identification of the radial glial cell as a key neuronal stem cell in the developing brain has helped shift attention to the role of glial cells as neuronal stem cells in the adult brain, and has the potential to lead to innovative therapies aimed treating diseases of brain injury.