Spike frequency adaptation (SFA) and rebound action potentials (RAPs) in hESMNs.

(A) An example of the change in instantaneous frequency during a train of action potentials evoked with positive current injection for 1 sec. Inset shows APs (upper) and injected currents (bottom). APs from which ‘a’ and ‘b’ ISI values were measure for SFA calculation are indicated. (B) SFA ratio, calculated as the maximum value of normalized ISIs after any amplitude of positive current injection, increased with DIV (n  = 8, R  = 0.73, P<0.05, Pearson’s linear regression). (C) RAPs were observed in a large subset of hESMNs. Upper trace shows voltage change after negative current injection. Bottom trace shows injected negative current steps. RAP follows the return of current to baseline after the hyperpolarizing step. (D) Incidence of RAPs in hESMNs at 4 different ages as indicated in Fig. 3 legend (n  = 29). Negative current steps with 5 pA increments (to at least 20 pA) were injected while checking for RAPs.