Abstract : In mouse neocortex, precursor cell divisions occur as soon as E11 and give rise to the first pioneers neurons, including Cajal-Retzius cells. Spontaneous electrical activity, supported by ion channels, is a key factor in central nervous system development. In the present work, the main goal was to understand how ion channels and calcium signalling are implicated in early neurogenesis. First, we found an inward sodium current in 55% of neuronal cells, including all Cajal-Retzius cells. At the same stage, we observed spontaneous calcium activity in proliferative and neuronal cells of cortical slices. We developed an imaging software statistically analyze calcium activity and to identify ions channels imvolved. While synapses were not yet formed, we observed the presence of synchronous calcium activity and early paracrine communication between cells. We demonstrated the existence of a signalling cascade: glycine receptors depolarization activate sodium channels expressed in neuronal cells, which in turn lead to cytoplasmic calcium increases via Na+/Ca2+ exchangers. The subsequent glutamate exocytosis paracrine release activate neocortical cells lacking sodium channels. The use of organotypic brain slice culture showed a major physiological implication of this original pathway in corticogenesis.