Figure 6.

Increasing the AHP reduces both the MMOs and the clockwise hysteresis in a real motoneuron. A1, Response to a slow triangular ramp of current (0.1 nA/s, 6.7 nA amplitude). Same arrangement as in Figures 1A, 2A. Note the substantial decrease of spike amplitude during the ascending ramp. The discharge was asymmetric, the derecruitment current being larger (3.8 nA) than the recruitment current (2.4 nA), i.e., the I–F relationship displayed a clockwise hysteresis (data not shown). A2, Magnification of the voltage (truncated spikes) showing the fast subthreshold oscillations and the irregularity of the discharge. B1, Response when an artificial AHP (conductance 0.4 μS) was added to the natural one using dynamic clamp. Note that the spike amplitude remained nearly constant throughout the ramp and that the clockwise hysteresis disappeared (equal recruitment and derecruitment currents). B2, Magnification of the voltage trace showing that the subthreshold oscillations were much reduced compared with the large oscillations observed without the artificial AHP. Moreover the discharge became much more regular. The input resistance of this motoneuron was 5.0 MΩ.