I_h expression in cultured adult SGNs. (A) Family of representative I_h traces from adult (≥P40, base) WT, Hcn1^−/−, and Hcn2^−/− SGNs. (B) Normalized I_h activation curves generated by fitting a Boltzmann function to tail currents shown in A. Note the hyperpolarized half-activation voltage shift in Hcn1^−/− SGNs compared with WT and Hcn2^−/−. (C and D) Summary of conductances (C) and half-activation voltages (D) for 11 WT, 6 Hcn1^−/−, and 11 Hcn2^−/− SGNs. (E) Summary of I_h fast activation time constants. Error bars equal +1 SD. **, P < 0.01; ***, P < 0.001.