Dynamics of the WCI system (Equations 9a-9c) at . (a)-(d) Time series of the voltage variable x at several values of k, with k decreasing from top to bottom. The traces in frames (a) and (b) are at the same value of k and illustrate bistability. (e) Bifurcation diagram upon variations of parameter k, including branches of fixed points (black curve) and periodic orbits (two red curves, indicating maximal and minimal values of x over the orbit). Solid/dashed curves indicate stable/unstable solutions. The torus bifurcation at is supercritical. At smaller values of k, direct numerical simulations show that the system exhibits bursting (□, indicating maximal and minimal values of x) and AM spiking (△, indicating extrema of the modulation envelope).