Basic principles for generating motor output in the stomatogastric ganglion.

The lobster stomatogastric ganglion contains 30 neurons and when modulated can produce two distinct rhythmic motor patterns--the gastric mill and the pyloric. The complete neural circuitry underlying both patterns is well known. Without modulatory input no patterns are produced, and the neurons fire tonically or are silent. When neuromodulators are released into the ganglion from specific neurons or are delivered as hormones, the properties of the neurons and synapses change dramatically and modulator-specific gastric mill and pyloric patterns are produced. In general the rhythmicity derives from the induced burstiness of the neurons, and the pattern from the strengths of the electrical and chemical synapses. The organized activity can be traced to a marked reduction of chaotic activity in individual neurons when they shift from the unmodulated to the modulated state.