Dependence of firing pattern on intrinsic ionic conductances: Sensitive and insensitive combinations

We construct maps of the intrinsic firing state (silent, tonically firing, or bursting) of a model neuron as a function of its maximal ionic conductances. The firing properties vary significantly only in response to changes in particular, sensitive combinations of conductances that may serve as targets for neuromodulation. Less sensitive combinations define directions along which neuronal conductances may drift without triggering significant changes in firing activity. This suggests that neurons may have similar functional properties despite widely varying conductance densities. (C) 2000 Elsevier Science B.V. All rights reserved.