For dissociating intact colonies of pluripotent stem cells from the layer of DR4 feeders, hiPSCs were exposed to a low concentration of dispase (Invitrogen: 17105-041; 0.7 mg/ml) for ~30 min. Suspended colonies were subsequently transferred into ultra-low-attachment 100 mm plastic plates (Corning) in hiPSC medium without FGF2. For the first 24 h (day 0), the medium was supplemented with the ROCK inhibitor Y-27632 (EMD Chemicals). For neural induction, dorsomorphin (also known as compound C; Sigma 10 μM) and SB-431542 (Tocris, 10 μM) were added to the medium for the first five days. On the sixth day in suspension, the floating spheroids were moved to neural medium (NM) containing Neurobasal (Invitrogen: 10888), B-27 serum substitute without vitamin A (Invitrogen: 12587), GlutaMax (Invitrogen, 1:100), 100 U/ml penicillin and 100 μl streptomycin (Invitrogen). The NM was supplemented with 20 ng/ml FGF2 (R&D Systems) and 20 ng/ml EGF (R&D Systems) for 19 days with daily medium change in the first 10 days, and every other day for the subsequent 9 days. To promote differentiation of the neural progenitors into neurons, FGF2 and EGF were
