Fig. 10. Post-spike increase in membrane conductance as revealed by passing steady current. (A) Single spikes evoked by a brief pulse (bars) while passing different intensities of steady current (black traces). Superimposed gray traces correspond to control spikes without passing current. Note the inversion of the after-hyperpolarization when the basal membrane potential surpassed –80 mV (horizontal broken line). (B) V/I plots obtained in another cell, before (open symbols), 5 ms after (gray symbols) and 10 ms after the spike (black symbols). The linear relationship 5 ms after the spike (gray symbols) indicates that the spike causes an increase in conductance similar to that caused by the tonic depolarization of the membrane 1 ms before the spike (open symbols).