Figure 4.

Neuron activity for three different levels of input. In each panel, the cubic shaped V -nullcline is shown in red, the sigmoid shaped h-nullcline in green. The location of their intersection determines the activity of the neuron. The trajectory is shown with a thick black dotted line from an initial condition indicated by a star. Threshold is indicated with a magenta vertical line, located at V = V_th=−50 mV. Double arrows indicate motion on the fast timescale, single arrows on the slow timescale. Blue arrows indicate the direction of the vector field, and the black dot indicates the critical point for the system in each case. (A) The neuron remains at a silent state for all time when the nullclines intersect on the left branch of the V -nullcline. (B) When the nullclines meet on the middle branch of the V -nullcline, bursting activity can occur since both knees are accessible. (C) Tonic activity results from the configuration in which nullclines intersect on the right branch of the V -nullcline.