LONG-TERM-MEMORY OF AN OPERANTLY CONDITIONED RESPIRATORY BEHAVIOR PATTERN IN LYMNAEA-STAGNALIS

The freshwater snail Lymnaea stagnalis breaths bimodally either throug h its skin (cutaneous respiration) or via a rudimentary lung opening c alled the pneumostome (aerial respiration), Aerial respiratory behavio ur can be operantly conditioned, Animals placed in an aquatic, hypoxic environment received a tactile stimulus to the pneumostome area every time they attempted to breathe, Over a period of five training sessio ns (2.5 days), the animals learned not to breathe, and the number of s timuli received in the fifth session was significantly lower than in t he first session. These changes in the respiratory behaviour following the operant paradigm were shown to persist for at least 24 h. We aime d to determine whether the changes in the learned behaviour would pers ist for longer, We obtained direct evidence that the behavioural chang es following operant conditioning persisted for at least 4 weeks follo wing the last training session. However, we found that the persistence of this memory was dependent upon the training procedure used. Memory persisted longer following a spaced training procedure (4 weeks) as o pposed to a massed training procedure (2 weeks). Yoked control animals showed no changes in their respiratory behaviour over the same time p eriods. However, if these yoked control animals were subjected to an o perant conditioning procedure, their ability to learn was not impeded. This study demonstrated that operant conditioning of a behaviour patt ern in a molluscan preparation can result in long-term memory and that the persistence of the memory is contingent on the training procedure used.