Mechanism for food avoidance learning in the central pattern generator of feeding behavior of Pleurobranchae californica.

Food-avoidance conditioning in the mollusk Pleurobranchaea results in suppression of the feeding response to food stimuli. In conditioned animals, identified interneurons of the central pattern generator (CPG) for feeding behavior, the Int-2s, respond to a food stimulus with greater and more long-lasting excitation than controls. Enhanced Int-2 responsiveness to food stimuli is associated with markedly heightened Int-2 excitability. Sustained activity in the Int-2s arrests motor output of the oscillatory CPG in the protraction/retraction movement cycle of feeding through tonic excitation of a population of retractor interneurons and inhibition of protractors. The CPG locus of the learning mechanism is permissive of sensory excitation of alternative behavior and leaves the possibility open for release of the suppressed behavior in a fully aroused state.