Fig. 4. Effects of lidocaine on biophysical properties of thalamocortical relay neurons. (A ) Effects of 100 μM lidocaine on the voltage dependence of activation of the I  ^hconductance (G  ^h; ordinate), calculated from the amplitudes of I  ^hpeak tail currents evoked by a repolarization to −78 mV. Tail current amplitudes were normalized to the maximum current levels obtained after the most negative prepulse (−128 mV) and plotted as a function of step potential (E ). Lidocaine decreased the slope factor but had no significant effect on the half-maximal activation potential (details, see Results, third paragraph); * = P < 0.05 (Student t  test). Effects of lidocaine on the kinetics of I  ^hactivation (B ) and deactivation (C ). (B ) Fast-time constants (τ) of activation plotted as a function of test voltages (E ) in control and in the presence of 100 μM lidocaine. (C ) Representative I  ^htail current (I ) relaxations upon repolarization to −78 mV after a hyperpolarization to −128 mV in control and in the presence of 100 μM lidocaine. All recordings were performed in the presence of 0.1 mM BaCl².