||Operant reward learning of feeding behavior in Aplysia increases the frequency and regularity of biting, as well as biases
buccal motor patterns (BMPs) toward ingestion-like BMPs (iBMPs). The engram underlying this memory comprises cells
that are part of a central pattern generating (CPG) circuit and includes increases in the intrinsic excitability of identified
cells B30, B51, B63, and B65, and increases in B63–B30 and B63–B65 electrical synaptic coupling. To examine the ways in
which sites of plasticity (individually and in combination) contribute to memory expression, a model of the CPG was developed.
The model included conductance-based descriptions of cells CBI-2, B4, B8, B20, B30, B31, B34, B40, B51, B52, B63,
B64, and B65, and their synaptic connections. The model generated patterned activity that resembled physiological BMPs,
and implementation of the engram reproduced increases in frequency, regularity, and bias. Combined enhancement of
B30, B63, and B65 excitabilities increased BMP frequency and regularity, but not bias toward iBMPs. Individually, B30 increased
regularity and bias, B51 increased bias, B63 increased frequency, and B65 decreased all three BMP features.
Combined synaptic plasticity contributed primarily to regularity, but also to frequency and bias. B63–B30 coupling contributed
to regularity and bias, and B63–B65 coupling contributed to all BMP features. Each site of plasticity altered multiple
BMP features simultaneously. Moreover, plasticity loci exhibited mutual dependence and synergism. These results indicate
that the memory for operant reward learning emerged from the combinatoric engagement of multiple sites of plasticity.