We used transcriptional profiling to assess the developmental maturity and the regional identity of hCSs at two distinct time points. We compared the transcriptional profiles of hCSs to those of the developing human fetal brain using a machine learning algorithm (CoNTExT)12 trained on 1,340 primary tissue samples. We observed a strong overlap between hCSs and cortical developmental stages up to late mid-fetal periods (19–24 PCW) (Fig. 1e). This is in contrast to monolayer methods as well as other 3D approaches for neural differentiation of hiPSCs6,12 that yield neurons mapping onto earlier fetal stages (Supplementary Fig. 2). We then looked for genes whose expression was changing in the same direction in hCSs and human fetal cortex between stages 1 and 2 (4–10 PCW) and stage 6 (19–24 PCW), but not in hiPSC-derived neural cultures differentiated in monolayer (Supplementary Table 1). Interestingly, upregulated genes were enriched for synaptic transmission genes (GO enrichment, P = 0.009), whereas the downregulated genes were enriched for cell cycle (P = 0.02) and cell division genes (P = 0.001). We next used transition mapping12 to assess the
