Human iNs were generated according to protocols described elsewhere27,29 with slight modifications. Briefly, iPSCs were seeded onto a Matrigel™-coated six-well plate at a density of 300,000 cells per well (Day –1) in mTeSR. Lentivirus and Y-compound (Y-27632; 5 μM) were added the following day (Day 0). To generate excitatory neurons, lentivirus expressing the transcription factor Ngn2 (with puromycin resistance) was added. For inhibitory neurons, viruses expressing Dlx2 (with hygromycin resistance) and Ascl1 (with puromycin resistance) were added. For dopaminergic neurons: Ascl1, Nurr1 and Lmx1a viruses were added. EN1, Foxa2 and Pitx3 were also added on Day 3. All of the factors utilized for the iN cell protocol were expressed under the TetO promoter (Tet-On), and thus, all infections included a virus expressing the reverse tetracycline-controlled transactivator (rtTA) protein. The following day (Day 1), the cultures were switched to Neurobasal media supplemented with B27 and L-glutamine. Doxycycline (2 ng/μl) was added on Day 1 to induce expression of subtype-specific transcription factors, along with Y-compound (5 μM) to limit apoptosis. On Day 2, iPSCs underwent a puromycin (1 μg/ml) selection. Day 3
