Basic oscillator model formed by a feedback loop between an excitatory unit and an inhibitory unit .
Small triangles indicate excitatory connections, and small circles inhibitory connections.
Figure 2 shows a typical limit cycle drawn on the x - y plane, as exhibited by a single oscillator. The two nullclines split the x - y plane into four regions. Within each region, and have unique signs. Thus, both x and y decrease in this region until the trajectory intersects with the x -nullcline. After the intersection, the trajectory moves into the lower-left region where and thus x starts to increase.