Operant conditioning is characterized by the contingent reinforcement of a designated behavior. Previously, feeding behavior in Aplysia has been demonstrated to be modified by operant conditioning, and a neural pathway (esophageal nerve; E n.) that mediates some aspects of reinforcement has been identified. As a first step toward a cellular analysis of operant conditioning, we developed an in vitro buccal ganglia preparation that expressed the essential features of operant conditioning. Motor

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... tterns that represented at least two different aspects of fictive feeding (i.e., ingestion-like and rejection-like motor patterns) were elicited by tonic stimulation of a peripheral buccal nerve (n.2,3). Three groups of preparations were examined. In a contingent-reinforcement group, stimulation of E n. was contingent on the expression of a specific type of motor pattern (i.e., either ingestion-like or rejection-like). In a yoke-control group, stimulation of E n. was not contingent on any specific pattern. In a control group, E n. was not stimulated. The frequency of the reinforced pattern increased significantly only in the contingent-reinforcement group. No changes were observed in nonreinforced patterns or in the motor patterns of the control and yoke-control groups. Contingent reinforcement of the ingestion-like pattern was associated with an enhancement of activity in motor neuron B8, and this enhancement was specific to the reinforced pattern. These results suggest that the isolated buccal ganglia expressed an essential feature of operant conditioning (i.e., contingent reinforcement modified a designated operant) and that this analog of operant conditioning is accessible to cellular analysis.