Neural networks can be directed to change their activity pattern when subjected to neuromodulation. We use modeling techniques to study neuromodulation of central pattern generators (CPGs) in the crab (C. borealis) stomatogastric ganglion (STG). The STG is innervated by projection neurons whose processes release neuromodulatory substances. The modulatory commissural neuron 1 (MCN1) is one such projection neuron whose activity elicits a gastric mill rhythm (GMR: freq ~ 0.1 Hz). The frequency of this GMR is strongly regulated by a synaptic input from the pyloric circuit (freq: ~ 1 Hz). Recent experimental work has shown that superfusion of the neuropeptide pyrokinin (PK) elicits a GMR in the isolated STG that mimics the MCN1-elicited GMR (Hertzberg et al., SFN Abstr 33:604.14). We build a 2D model of the MCN1-elicited rhythm that exploits the difference in time scales operating within the asymmetric, reciprocally inhibitory CPG of the GMR. We then remove the MCN1 input and investigate what types of currents,...