The stomatogastric ganglion of the spiny lobster contains only 30 cells and generates two different motor patterns to operate striated stomach muscles. The synaptic circuitry of the ganglion is almost completely worked out. The proposed work includes a quantitative behavioral description in which axonal spike activity, neuromuscular physiology and movements are correlated. We want a good description of the dynamic range of burst patterns which occur in vivo. We are working out the mechanism of burst formation by selectively removing, or altering the activity of key cells in the circuit. Finally we are studying the turning on, turning off and modulatory effects of hormones and sensory nerve stimulation.