Figure 5. Simulated impalement can alter firing properties. A, Impact of injected current and impalement conductance, gimp, on firing properties. Voltage response of a model cell to subthreshold (i) and suprathreshold (ii) current injection after gimp is set to 7 nS, analogous to a microelectrode recording. Only phasic firing is observed. iii, Repetitive firing is observed when gimp is set to 0 nS, analogous to a whole-cell recording. When gM is removed from the model, the same parameters used in i, ii lead to non-firing (iv) and repetitive firing (v). B, Shaded regions indicate the set of all parameters which lead to non-firing (N, red), phasic firing (P, blue), and repetitive firing (R, black/gray). At gimp = 0 nS, the model neuron transitions rapidly from N to R, and repetitive firing results from any current injection above ∼20 pA. At gimp = 7 nS, the model neuron transitions from N to P at around 200-pA current injection, and repetitive firing is not observed for injected current less than 500 pA. C, same as B with gM set to 0 nS. Removing IM from the model by setting gM = 0 nS eliminates phasic firing altogether, i.e., cells transition directly from N to R regardless of impalement conductance. Open circles in B, C indicate the gimp and injected current values used to generate traces in A. Standard model with gleak = 0.5 nS.