Spike threshold and corresponding biophysical basis produced by realistic model.

<p>(A) Activation curves and kinetics of ionic currents for each cell type. There are three ionic currents, i.e., <i>I</i>_Na, <i>I</i>_Sub and <i>I</i>_K,dr, in three-dimensional model. The steady-state activations and voltage-dependent time constants of these currents are all the same for Type I (green solid line) and Type II (red dotted line) neurons. (B) Membrane currents at the subthreshold potentials. For two cell types, the subthreshold properties of <i>I</i>_Na, steady-state <i>I</i>_K,dr (i.e., <i>I</i>_K,dr,SS) and <i>I</i>_Leak are identical, while the direction and magnitude of <i>I</i>_Sub is different. It is inward in Type I neuron and outward in Type II neuron, which makes Type II neuron have a much larger outward <i>I</i>_SS at the threshold potentials. (C) Spike threshold within a range of d<i>V</i>/d<i>t</i> for each cell type. The d<i>V</i>/d<i>t</i> range is from 0.6mV/ms to 4.5mV/ms, since there is the delayed loss of stability appearing in Type II neuron with. d<i>V</i>/d<i>t</i><0.6mV/ms.