Mechanisms of Firing Patterns in Fast-Spiking Cortical Interneurons
Figure 5
Bifurcation Diagrams and the Fast–Slow Analysis of the Model Neuron
(A–C) are for small and (D–F) for large Na+ window currents. Parameters in (A–C) are as in Figure 2C: θm = −24 mV, gd = 0.39 mS/cm2, Iapp = 3.35 μA/cm2. Parameters in (D–F) are as in the top panel in Figure 3B: θm = −28 mV, gd = 0.39 mS/cm2, Iapp = 1.25 μA/cm2.
(A,D) The bifurcation diagram of the fast subsystem in the V-b space.
(B,E) The frequency f of the limit cycle of the fast subsystem, plotted as a function of b (f-b curves).
(C,F) The functions b∞(VFP(b)) and F(b) (Equation 2) plotted as a function of b. Thin solid lines: stable fixed points; thin dotted lines: unstable fixed points; thick solid line: stable limit cycle (periodic state); thick dotted line: unstable limit cycle. Solid circles denote Hopf, saddle-node (SN), and saddle-node of periodics (SNP) bifurcation points. The value of b at rest (Iapp = 0) is brest, and b* is the value of b at steady state of the neuron. For bdelay, see text. In (C,F), the intersection of the curve b = F(b) with the diagonal dashed line determines the value of b* (open square point). Arrows represent the evolution of the neuron from rest to its steady state following a current step injection of amplitude Iapp.