Fig. 3

Continuation for increasing $g_{\mathrm{SI}}$ of solutions to system (5)-(8). Panel (a) shows the Auto$L_2$-norm <abbrgrp>5556</abbrgrp> of the solution branch versus $g_{\mathrm{SI}}$ and illustrates that the spike-adding mechanism happens suddenly via a pronounced drop in norm; panels (b) (c) (d) (e) and (f) show representative solutions along the branch, indicated by the correspondingly labelled dots in panel (a), and illustrate that solutions during a spike generation, i.e., panels (c) and (d), exhibit a stretched ADP that develops into a double step before relaxing back to the resting potential.