Fig. 1.

Schematic diagram of the different preparations used in this study. A, Isolated AB or PD neurons (descending modulatory inputs were either blocked by a tetrodotoxin block on the stomatogastric nerve or kept intact). B, An AB–PD (1) or AB–2xPD (2) pacemaker subnetwork (with or without descending inputs).C, The intact pyloric circuit (modulatory inputs were kept intact). An example of the method of isolating neurons and subnetworks is also shown in C. To isolate the AB–PD subnetwork (shown in B1), the VD neuron and one PD neuron were photoinactivated, and the LP → PD synapse was pharmacologically blocked with picrotoxin. All synaptic connections are either electrical (nonrectifying synapses, resistors; rectifying synapses, diodes) or chemical inhibitory (small circles).