In vitro analog of operant conditioning in Aplysia. II. Modifications of the functional dynamics of an identified neuron contribute to motor pattern selection

Previously, an analog of operant conditioning was developed using the bucca l ganglia of Aplysia, the probabilistic occurrences of a specific motor pat tern (i.e., pattern I), a contingent reinforcement (i.e., stimulation of th e esophageal nerve), and monotonic stimulation of a peripheral nerve (i.e., n.2,3). This analog expressed a key feature of operant conditioning (i.e., selective enhancement of the probability of occurrence of a designated mot or pattern by contingent reinforcement). In addition, the training induced changes in the dynamical properties of neuron B51, an element of the buccal central pattern generator. To gain insights into the neuronal mechanisms t hat mediate features of operant conditioning, the present study identified a neuronal element that was critically involved in the selective enhancemen t of pattern I. We found that bursting activity in cell B51 contributed sig nificantly to the expression of pattern I and that changes in the dynamical properties of this cell were associated with the selective enhancement of pattern I. These changes could be induced by an explicit association of rei nforcement with random depolarization of B51. No stimulation of n.2,3 was r equired. These results indicate that the selection of a designated motor pa ttern by contingent reinforcement and the underlying neuronal plasticity re sulted from the association of reinforcement with a component of central ne uronal activity that contributes to a specific motor pattern. The sensory s timulus that allows for occurrences of different motor acts may not be crit ical for induction of plasticity that mediates the selection of a motor out put by contingent reinforcement in operant conditioning.