Interestingly, we observed a consistent difference in electrophysiological maturation of NKX2.1+ cells plated on mouse versus human cortical feeders as shown in Table S2. Recordings were obtained at either 14–16 DIV or 20–30 DIV for the mouse feeder condition, and 20–30 DIV for the human cortical feeder condition. Analysis of the basic electrophysiological properties of both the 10 to 18 and 6 to18 groups plated on mouse feeders showed more mature characteristics at later time-points of differentiation. There was significant hyperpolarization of the resting membrane potential (RMP) with time, as well as a decrease in the input resistance (Ri). In addition, the action potentials became faster and narrower as evidenced by the decrease in the rise time and half width. In contrast, GFP+ neurons from the day 10-18 condition that were recorded 20–30 days after plating on the human feeder layer retained relatively immature characteristics, comparable to the measurements seen in the younger 14–16 DIV neurons plated onto a mouse feeder layer. The RMP, action potential rise time, action potential half width, and input resistance were significantly different in the
