A training protocol was developed to classically condition feeding behavior
in Aplysia californica using tactile stimulation of the lips as the condit
ional stimulus (CS) and food as the unconditional stimulus (US). Paired tra
ining induced a greater increase in the number of bites to the CS than unpa
ired training or US-only stimulation. Memory for classical conditioning was
retained for at least 24 hr. The organization of the reinforcement pathway
that supports classical conditioning was analyzed in additional behavioral
experiments. No evidence was found for the contribution to appetitive rein
forcement of US-mediating pathways originating in the lips of the animals.
Bilateral lesions of the anterior branch of the esophageal nerve, which inn
ervates parts of the foregut, however, were found to attenuate classical co
nditioning. Thus, it appears likely that reinforcement during appetitive cl
assical conditioning of feeding was mediated by afferent pathways that orig
inate in the foregut. The companion paper (Lechner et al., 2000) describes
two neurophysiological correlates of the classical conditioning.