Patch clamp recordings were performed on human ESC-derived neurons of the DCX-Cit reporter line. At 65–75 days post-induction the culture dishes were transferred to the stage of an upright microscope equipped with differential interference contrast optics and perfused at 3–4 mL per minute with artificial cerebrospinal fluid (aCSF) bubbled with carbogen gas (95% O2/5% CO2). The aCSF was composed of: 121 mM NaCl, 2.5 mM KCl, 1.25 mM NaH2PO4, 26 mM NaHCO3, 12.5 mM glucose, 5 mM HEPES, 2 mM CaCl2.2H2O 2, and 2 mM MgSO4.7H2O with pH of 7.35 and osmolality of 305 mMol/Kg. Cells were patched based on healthy appearance, shape of somata, and Cit fluorescence. Borosilicate glass electrodes had a tip resistance of 4–6 MOhms when filled with the internal pipette solution composed of: 130 mM K-Gluconate, 4 mM KCl, 10 mM HEPES, 0.3 mM EGTA, 10 mM Na2-phosphocreatine, 4 mM Mg-ATP, and 0.3 mM Na2-GTP adjusted to pH 7.35 and osmolality of 285–290 mMol/Kg. Recordings were obtained with a Multiclamp 700B amplifier and Digidata 1550 digitizer using pClamp10 data acquisition software (Molecular Devices). Action potential firing
