Fig. 4.

Modeled neurons have current-step evoked firing patterns that depend on the maximum conductance of g_KL and g_Na. Responses are shown at the lowest current step (current threshold ±0.5 pA) that yielded an action potential. Left column: models with g_KL = 0 exhibited continual spiking throughout the duration of the current step. Smaller values of g_Na produced shorter action potentials. At the lowest value of g_Na (bottom row), full action potentials did not form and the modeled neuron responded with sustained voltage oscillations. Interspike/interoscillation intervals varied little during the simulation time and averaged ∼40 ± 0.5 ms (14 intervals were pooled across all responses in left column). Middle column: adding g_KL to the model produced accommodation to the firing patterns with the amplitude and number spikes generated decreasing with continued current injection. At any fixed value for g_Na (e.g., 10 mS/cm²), the addition of g_KL hyperpolarized the resting membrane potential and increased the current amplitudes needed to initiate spiking (across all 3 columns, current threshold increased from 10 to 80 pA). The presence of g_KL also made the first action potential larger and faster and the timing between adjacent action potentials shorter than in left column, where g_KL was missing. On average, the interspike/interoscillation intervals were 16 ± 0.4 ms (13 intervals were pooled across all responses in middle column). Right column: at g_KL=1.1 mS/cm² (the largest value used), the model responded with a single action potential for all current steps applied.