Model 1a, I-NaP and I-KM sensitivites
To examine the sensitivity of the model to the balance between I-NaP and I-KM, an extensive parameter space search was performed (holding all parameters fixed except I-NaP and I-KM). Contour plots of spike number as a function of the maximum conductances for these two currents at varying input delays reveal a response topology of relatively invariant shape that translates toward areas of increased maximum I-NaP conductance and decreased maximum I-KM conductance as the delay goes from 0 to 6ms (figures 10a, 10b). It is apparent from these figures that the temporal sensitivity of the spike number response to delay time results (in part) from the model’s location (I-NaP=100%, I-KM=100%) atop a steep gradient on the parameter contour surface. This gradient extends bidirectionally toward areas of either increased I-NaP and I-KM maximum conductances or decreased I-NaP and I-KM maximum conductances, while most other areas on the contour surface lack a sufficient, properly directed gradient to support the desired relationship between spike number and delay. Thus, the model is quite sensitive to small independent changes in either of these two conductances although its desired response remains robust while the ratio between the two conductances remains relatively constant.
