Fig. Fig.5b5b shows the resulting bifurcation diagram when r=1. We have Z-shaped curve of inhibitor Wortmannin fixed points. For larger values of ��, there are three fixed points; the lower fixed point is stable, the middle is a saddle, and the upper is unstable. As �� decreases, lower stable and middle saddle fixed points merge at a saddle-node bifurcation (labeled SN). There is also a subcritical Hopf bifurcation point on the upper branch and fixed points become stable once passed this point (thick black). A branch of unstable periodic orbits (thin gray), which turn to stable orbits (thick black), emanates from the Hopf bifurcation point, and becomes a saddle-node homoclinic orbit when ��=��SN. In fact, this bifurcation structure persists for each r on [0, 1].
We trace the saddle-node bifurcation point (SN) in the bifurcation diagram as r varies to get a two dimensional bifurcation diagram, which is shown in Fig. Fig.6a.6a. We call the resulting curve ��-curve (the curve in the (��, r) plane at Fig. Fig.6a).6a). The fast subsystem shows sustained spiking in the region left to �� (spiking region) and quiescence in the region right �� (silent region). Note that if r is sufficiently small, then, we cannot get an oscillatory solution. Fig. Fig.6a6a also shows frequency curves (dependence of frequency of spikes on the total synaptic input �� for different values of r) in the spiking region. Fig. Fig.6b6b provides another view of these curves. There is a band-like region of lower frequency along ��, visible in the frequency curve when r=0.25.
This band is more prominent along the lower part of �� and this will play an important role in the generation of overlapped spiking. Figure 6 The frequency of firing in dependence on the slow variables �� and r. (a) ��-curve (gray line in the (��, r) plane) divides the space of the slow variables (��, r) into silent and sustained spiking regions. Over the sustained … Regular out-of-phase bursting solutions in the phase plane of slow variables and linear stability under constant calcium level Fig. Fig.77 shows the two parameter bifurcation diagram with the projection of regular 2-spike out-of-phase bursting solution when gsyn=0.86. Without loss of generality, let��s assume that active cell is cell 2 and silent cell is cell 1. We will follow trajectories of both cells from the moment when cell 2 fires its second spike.
Upper filled circle in Fig. Fig.77 denotes (��1, r1) of cell 1 and lower filled circle denotes (��2, r2) of cell 2 at this moment. Figure 7 Two-parameter bifurcation diagram with projection GSK-3 of 2-spike out-of-phase bursting solution. The close-to-vertical curve in the middle of the figure is the ��-curve shown in Fig. Fig.66 when [Ca]=0.7. The moment when active … First note that synaptic variable s of a cell rises once membrane potential rises, passes certain threshold (��g), and stays above it; s decreases otherwise (Eq. 4).