Identification of the neural pathway for reinforcement of feeding when Aplysia learn that food is inedible.

Bilateral sectioning of the esophageal nerves that innervate the gut of Aplysia was found to have profound effect on response decrement to inedible food: Time to criterion for cessation of feeding was elevated, no memory of the decrement was present 24 hr after training, and motor patterning during training was altered. The parametric features of response decrement to sustained lip stimulation were examined to determine their resemblance to parameters of response decrement to inedible food after esophageal nerve sectioning. Parameters of response decrement were similar, indicating that after esophageal nerve sectioning response decrement is likely to be the result of sustained lip stimulation. Bilateral nerve sectioning had no effect on decrement due to sustained lip stimulation. Unilateral lesions and lesions of either of the two major divisions of the esophageal nerves had no effect on learning that food was inedible. The data indicate that bilateral nerve sectioning eliminates all stimuli causing negative reinforcement of feeding due to failure to consume food. Based on the data in this and the previous paper, a model is presented suggesting sites of action and mechanisms for learning that foods are edible or inedible in Aplysia.