Parametric features of habituation of swim cycle number in the marine mollusc Tritonia diomedea

When repeatedly elicited, the oscillatory escape swim of the marine mollusc Tritonia diomedea undergoes habituation of the number of cycles per swim. Because the neural circuit for this behavior is reasonably well understood, a cellular analysis of habituation in Tritonia is feasible. Since such a study must ultimately relate cellular correlates to behavioral modifications, we have sought to increase our understanding of the parametric features of cycle number habituation in Tritonia. Habituation was compared when using different intertrial intervals, repeated training sessions, and different stimulus locations. Stimulus site generalization of habituation was demonstrated, suggesting that at least one site of plasticity underlying habituation is located postsynaptic to the sensory neurons for the response. Dishabituation from an above-zero baseline response level was not obtained. An isolated brain preparation was tested as a potential simplified system for cellular studies of habituation mechanisms. Repeated stimulation of a nerve containing sensory afferent processes resulted in a progressive reduction of swim motor program cycle number, with a rate similar to that seen in the behavior. Together, these findings: (1) establish a set of parametric features of cycle number habituation to be explained by physiological studies; (2) suggest that at least one circuit modification underlying the habituation is located among the circuit interneurons; and (3) indicate that the isolated brain preparation may serve as a useful neural analogue for studies of the cellular mechanisms of cycle number habituation in Tritonia. (C) 1996 Academic Press, Inc.