We are elucidating a novel cellular mechanism underlying sensorimotor integration as part of our characterization of how the gastropyloric receptor (GPR), an identified proprioceptor neuron, influences the gastric mill (chewing) CPG in the stomatogastric ganglion of the crab Cancer borealis. We elicit the gastric mill rhythm by selective stimulation of MCN1, a projection neuron that excites the reciprocally inhibitory neurons (LG, Int1) that form the core of the gastric mill CPG (Bartos et al, J Neurosci 1999). Rhythmic GPR stimulation that mimics its in vivo activity pattern selectively prolongs the retractor (Int1 active; LG inactive) phase of the gastric mill rhythm. Our previous work suggested that this effect is likely mediated either by GPR excitation of Int1 or by its presynaptic inhibition of MCN1 (Beenhakker & Nusbaum, SFN Abstract 2004). We tested the ability of each of these two synaptic actions to selectively prolong the retractor phase by using both computational modeling (Nadim et al, J Neuro...