NONASSOCIATIVE LEARNING-PROCESSES AFFECTING SWIMMING PROBABILITY IN THE SEASLUG TRITONIA-DIOMEDEA - HABITUATION, SENSITIZATION AND INHIBITION

The role of nonassociative learning processes in determining whether o r not a chemical stimulus will elicit the Tritonia diomedea swimming r esponse was examined in a variety of conditioning experiments. Iterati ve presentation of a chemical stimulus resulted in a reduced swimming probability (SP). By the criteria of Thompson and Spencer (Thompson RF , Spencer WA. Psychol. Rev. 1966;73:16-43) and others, this iterative reduction of SP was concluded to be the result of habituation. Site-sp ecificity and a below zero effect implicated sensory pathways in habit uation memory storage. The iterative reduction in SP was reversible, c onfirming that a sensitization-like process can also influence SP. It was further concluded that a short-term decrement in swimming cycle nu mber was most likely due to a constraint in the effector pathway. Expe rience with a tactile stimulus had a long-lasting decremental effect o n SP. This heterostimic reduction of SP was amplified in a multistimic paradigm that included both chemical and tactile stimuli during train ing. The chemical stimuli alone did not alter SP in this experiment. M ultistimic reduction lasted for a week and was reversed temporarily by an excitatory chemical stimulus. The long-lasting reduction of SP by tactile stimulation appears to be the result of a novel nonassociative inhibitory process, which was distinguished from other learning proce sses by its duration and specificity. A total of three distinct learni ng processes are postulated to account for the role of simple types of experience in determining SP in Tritonia: habituation, sensitization, and nonassociative inhibition. (C) 1998 Elsevier Science B.V. All rig hts reserved.