The impact of sucrose-derived unconditioned and conditioned negative feedback on the microstructure of ingestive behavior.

We describe at the microstructural level the impact of unconditioned and conditioned negative feedback on the licking behavior of the rat. Seven groups of rats were trained to ingest one of seven different concentrations of sucrose (0.025, 0.05, 0.1, 0.2, 0.4, 0.6, and 0.8 M sucrose) under real-feeding conditions until intake was stable. They were then given three sham-feeding tests with the same solution. We compared the size of the clusters (SC) and number of clusters (NC) during the 17-min period when intake rate was declining in the real-feeding test with SC and NC during the corresponding 17-min period in the following sham-feeding test. Intake increased significantly over the three sham-feeding tests with the three highest concentrations, indicating the extinction of conditioned negative feedback. With these three solutions, we compared the microstructure of licking behavior in the first with that in the third sham-feeding test to determine if conditioned negative feedback affected SC or NC or both. The effect of both unconditioned and conditioned negative feedback on licking behavior was to decrease the NC without significantly affecting their size. We conclude that negative feedback derived from the accumulation of sucrose in the gastrointestinal tract decreases the probability of initiating a bout of licking during a pause. It has no effect on the ability to continue a bout of licking once it has begun.