Classical Conditioning of Feeding inAplysia: I. Behavioral Analysis

Abstract

A training protocol was developed to classically condition feeding behavior in Aplysia californica using tactile stimulation of the lips as the conditional stimulus (CS) and food as the unconditional stimulus (US). Paired training induced a greater increase in the number of bites to the CS than unpaired 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 reinforcement of US-mediating pathways originating in the lips of the animals. Bilateral lesions of the anterior branch of the esophageal nerve, which innervates parts of the foregut, however, were found to attenuate classical conditioning. Thus, it appears likely that reinforcement during appetitive classical conditioning of feeding was mediated by afferent pathways that originate in the foregut. The companion paper () describes two neurophysiological correlates of the classical conditioning.

Cognition in Invertebrates

“…Changes in neuronal activity and cellular properties that were recorded following tactile conditioning occur at all levels of the system, including central sensory pathways, modulatory interneurons, central pattern generator (CPG) interneurons, and motoneurons involving several possible plasticity sites. Aplysia biting behavior can be conditioned similarly (Lechner et al, 2000a(Lechner et al, , 2000b. A brief touch to the lips with a small brush (CS) does not usually elicit a bite.…”

“…It was described above how the feeding behavior of Aplysia can be conditioned classically and operantly (Nargeot et al, 1997(Nargeot et al, , 1999a(Nargeot et al, , 1999b(Nargeot et al, , 1999cLechner et al, 2000aLechner et al, , 2000bBrembs et al, 2002Brembs et al, , 2004Brembs, 2003aBrembs, , 2003bMozzachiodi et al, 2003). Taking advantage of the greater physiological accessibility, a reduced preparation of the isolated buccal and cerebral ganglia was used.…”

Operant conditioning in invertebrates

“…Early on, the esophageal nerve appeared to be crucial for the effectiveness of these conditioning experiments [31,38,39]. Recording extracellularly from the esophageal nerve in the intact animal during a biting movement that fails to grasp food reveals little activity.…”

Context Learning and the Effect of Context on Memory Retrieval in Lymnaea

“…Thus although the internal state of the animal may have been altered by the lack of food, this alteration in state only had a negative impact on learning and memory when a specific training context (food odorant) was used. As in appetitive classical conditioning studies using Lymnaea Staras et al 1999), other mollusks (Susswein et al 1986;Lechner et al 2000) and vertebrates (Dickinson 1980) the internal state of the animal greatly influences the establishment of learning. For instance, it is much more difficult to associatively condition a well-fed animal to a neutral or repulsive stimulus than it is with a hungry animal (Dickinson 1980).…”