Flavor-postingestive consequence associations incorporate the behaviorally opposing effects of positive reinforcement and anticipated satiety: implications for interpreting two-bottle tests.

Rats consuming distinctively flavored solutions containing different numbers of calories learn to associate each flavor with the ensuing postingestive effects ("flavor-postingestive consequence learning"). The hallmark of such learning is preferential consumption of one of the flavors in two-bottle tests (both flavors presented in nutrient-identical solutions). Two experiments were conducted to characterize the relationship between the number of calories associated with flavors and subsequent preferences in two-bottle tests. In Experiment 1, three groups of rats each associated distinctive flavors with real-fed sugar and with sham-fed sugar. The groups differed in the concentration of sucrose (8%, 14%, 24%) with which they were trained. In two-bottle tests rats trained with 8% sucrose preferred the real-fed flavor, whereas rats trained with 24% sucrose preferred the sham-fed flavor. Rats trained with 14% sucrose were intermediate to the other groups. In Experiment 2, two groups of rats associated distinctive flavors with two concentrations of real-fed sucrose. In two-bottle tests, the group trained with 1% and 5% sucrose preferred the flavor paired with the higher concentration, whereas the group trained with 5% and 30% sucrose preferred the flavor paired with the lower concentration. These findings suggest that flavor-postingestive consequence learning incorporates both positive reinforcement, which has the behavioral effect of increasing intake of the associated flavor, and anticipated satiety, which has the behavioral effect of suppressing intake of the associated flavor. When a flavor is associated with relatively few calories, the positive reinforcing effect predominates over anticipated satiety. However, when a flavor is associated with a greater number of calories, anticipated satiety predominates over the positive reinforcing effect.