Fig. 5.

Orbit segments ${\mathbf{u}}_{\mathrm{OFF}}(t)$ of the boundary value problem (5)-(8). Orbit segments ${\mathbf{u}}_{\mathrm{OFF}}(t)$ for $g_{\mathrm{SI}}\approx 0.5615{\text{mS/cm}}^2$ overlayed on the critical manifolds of Figure 4 with $g_{\mathrm{SI}}=0.5615{\text{mS/cm}}^2$. The orbit segments are selected along the first downward peak in Figure 3a; panel (a) shows an orbit segment just before the minimum of the peak in Figure 3a is reached; panel (b) shows one shortly after; panel (c) shows the orbit segments labelled (d) in Figure 3a; and panels (d), (e) and (f) show the spike generation as the orbit segments are continued until the start of the next ‘plateau’ in Figure 3a.