Persistent and resurgent Na+ currents have an increased prevalence by hearing onset. A, Representative Na+ currents elicited in basal and apical SGNs, at developmental stages before (P6) and after the onset of hearing (P14, P21, P80). TTX-sensitive difference currents were elicited using the voltage protocol in Figure 3A. B, Scatter plot of INaR/INaT ratios for individual SGNs at various developmental ages. C, Variations in INaR/INaT at different tonotopic locations. Individual data from B has been grouped (P0-P1, P3, P5, P6, P8, P12-P14, P21, and P80-P90) and separated into tonotopic origin (base, mid, and apex). D, Mean INaR/INaT ratio for all SGNs (basal and apical cells pooled) plotted as a function of test potentials at various developmental ages (P6, n = 9; P12-P14, n = 30; P80-P90, n = 12). E, Mean INaP/INaT ratio plotted as a function of test potentials, for the same cells as in D.