The process in which neuroepithelial cells in the neural tube acquire specialized structural and/or functional features of basal progenitor cells, neuroblasts that lose their contacts with the ventricular surface. Differentiation includes the processes involved in commitment of a cell to a specific fate. [ GOC:dph http://www.ncbi.nlm.nih.gov/pubmed/16226447 GOC:jid GOC:cls http://purl.obolibrary.org/obo/go/references/0000021 GOC:dgh ]