Figure 3. Relationship between ion channel densities and spiking pattern.

A, systematically co‐varying ${\overline{g}}_{\mathrm{K},\mathrm{lt}}$ and ${\overline{g}}_{\mathrm{K},\mathrm{A}}$ revealed that distinct regions in this 2‐D parameter space yield different spiking patterns. Boundaries shown here are based on testing with I _stim  = 60 μA cm⁻². Traces in a–d show sample responses for parameter values labelled on the main plot. Large parameter variations that remain within a region yield the same spiking pattern; compare condition a (${\overline{g}}_{\mathrm{K},\mathrm{lt}}$ = 3 mS cm⁻², ${\overline{g}}_{\mathrm{K},\mathrm{A}}$ = 4 mS cm⁻²) with condition b (${\overline{g}}_{\mathrm{K},\mathrm{A}}$ increased by 4 mS cm⁻²). In contrast, small parameter variations that cross a boundary yield different spiking patterns; compare condition a with condition c (${\overline{g}}_{\mathrm{K},\mathrm{A}}$ reduced by 0.5 mS cm⁻²) or condition d (${\overline{g}}_{\mathrm{K},\mathrm{lt}}$ increased by 0.5 mS cm⁻²). B, boundaries can shift because of stimulus intensity (I _stim), meaning a neuron with fixed values of ${\overline{g}}_{\mathrm{K},\mathrm{lt}}$ and $\overline{g}$ _K,A can exhibit different spiking patterns at different I _stim. To illustrate, each vertical arrow on the left panel represents a neuron: for neuron a, ${\overline{g}}_{\mathrm{K},\mathrm{lt}}$ = 3 mS cm⁻² and ${\overline{g}}_{\mathrm{K},\mathrm{A}}$ = 4 mS cm⁻²; for neuron b, ${\overline{g}}_{\mathrm{K},\mathrm{lt}}$ = 3.5 mS cm⁻² and ${\overline{g}}_{\mathrm{K},\mathrm{A}}$ = 2.5 mS cm⁻². The spiking pattern at each I _stim (illustrated on the right) depends on which region the arrow passes through. C, boundaries can also shift because of pre‐stimulus membrane potential. For these simulations, a subthreshold ‘pre‐pulse’ (I _pre) was used to vary the membrane potential before the onset of suprathreshold stimulation. Each plane represents the response to I _stim  = 60 μA cm⁻² after a different pre‐pulse (pre‐stimulus membrane potential is indicated beside each voltage trace). The vertical arrow represents a neuron with ${\overline{g}}_{\mathrm{K},\mathrm{lt}}$ = 2 mS cm⁻² and ${\overline{g}}_{\mathrm{K},\mathrm{A}}$ = 6 mS cm⁻². Traces on the right show the reduced availability of g _K,A depending on I _pre. By partially inactivating g _K,A, subthreshold depolarization reduces the availability of those channels for activation during suprathreshold stimulation, effectively re‐scaling the y‐axis.