Figure 7.

Counterclockwise hysteresis in the model. A, The time constant of the slow inactivation of the sodium current was reduced to 0.6 s and the AHP conductance set to 0.1 μS. Top, Voltage response; middle, slow inactivation variable; bottom, injected current. A few spikes only were emitted and they were followed by sustained fast oscillations as shown on the enlargement of the circled area. B1, The AHP conductance was increased to 1 μS. Same arrangement as in Figure 7A1. Note that there is less slow inactivation than in A and that the discharge is sustained. The gray dots on the inactivation curve indicate the values of hs at recruitment and derecruitment. B2, I–F curve. Note the counterclockwise hysteresis. B3, Magnification of the voltage response at the transition from the subprimary range (SPR) to the primary firing range (PR).