To investigate the hSS-derived neurons that migrated into hCS, we examined their single cell transcriptome at 4 weeks after assembly (Fig. 4a). t-SNE analysis indicated 3 clusters (Fig. 4b), with Dlxi1/2b::eGFP+ cells in hSS distributed primarily in cluster A, while Dlxi1/2b::eGFP+ cells migrated into hCS primarily distributed in clusters B and C (Fig. 4c). Cells in all clusters expressed similar levels of GAD1 and CELF4, but cluster B and C down-regulated the subpallial marker PBX3 (Extended Data Fig. 6c; Supplementary Table 4). Migrated cells displayed expression changes in genes previously associated with interneuron migration, including ERBB4, NNAT, MALAT1, SOX11 and NXPH129,30 (Fig. 4d). These neurons also had higher levels of activity-dependent genes, including FOS, the AMPA-receptor trafficking regulator GRIP231 and IGF132, as well as the disease-related genes RASD133, TCF434 (Fig. 4d; Extended Data Fig. 6c). We next examined dendrites of Dlxi1/2b::eGFP+ cells in hSS and in fused hSS-hCS. We found that hSS-derived cells that moved into hCS increased the complexity of their branching (Fig. 4e; Extended Data Fig. 10a, b). We then measured their electrical properties in hSS before and
