NEUROPHYSIOLOGICAL CORRELATES OF UNCONDITIONED AND CONDITIONED FEEDING-BEHAVIOR IN THE POND SNAIL LYMNAEA-STAGNALIS

We used a behavioral appetitive learning paradigm followed by electrop hysiological analysis to investigate the neuronal expression of appeti tive conditioning in Lymnaea. We first established the levels of uncon ditioned and conditioned feeding responses in intact animals. We then demonstrated that neuronal correlates of both unconditioned responses to touch and food and a conditioned response to touch could be found i n semiintact preparations of the same animals that had been subjected to behavioral tests and conditioning trials. In the conditioning exper iments, the experimental animals received 15 trials in which touch to the lips, the conditioned stimulus (CS), was paired with sucrose, the unconditioned food stimulus (US). Control animals received 15 presenta tions of either CS or US, or both, applied in a random manner. After t raining, a strong conditioned response to touch was established in the experimental but not in the control groups. For subsequent electrophy siological analysis of posttraining neuronal responses to the touch CS , semi-intact preparations were set up from the same animals that had been behaviorally conditioned or subjected to control procedures. Intr acellular recordings, made from previously identified motoneurons of t he feeding system, allowed the fictive feeding response to the CS to b e monitored. In experimental preparations, touch applied to the lips e voked significantly more fictive feeding cycles than in controls, and this demonstrated the existence of a neurophysiological correlate of t he appetitively conditioned response observed in the whole animals.