Learning, memory and a respiratory central pattern generator

In an attempt to elucidate the causal mechanisms underlying learning and memory we have developed a model system, aerial respiration in the pond snail Lymnaea stagnalis. A three-neuron central pattern generator (CPG) whose sufficiency and necessity have been demonstrated mediates this behaviour. Aerial respiration, while an important homeostatic behaviour, is inhibited by the activation of the whole body withdrawal response that the animal uses to protect itself. We found that it was possible to operantly condition snails not to perform aerial respiration in a situation, a hypoxic environment, where aerial respiration should predominate. Operant conditioning was achieved by eliciting the pneumostome withdrawal response, part of the whole body withdrawal response, each time the animal attempted to open its pneumostome to breathe. Yoked control animals did not demonstrate an alteration in breathing behaviour. Subsequently we determined neural correlates of this associative behaviour and found that neuronal changes are distributed throughout the CPG. This preparation may afford us the opportunity to determine the casual neuronal changes that underlie learning and memory of associative conditioning.