Evidence that oral and nutrient reinforcers differentially condition appetitive and consummatory responses to flavors

Rats tend to increase their intake of a flavor that has previously been paired with either sweet taste or with caloric repletion. However, it is unclear whether such a change in intake is caused by changes in appetitive behaviors such as orienting and approach, or changes in consummatory behaviors and oral responsiveness. Also, it is unclear whether oral reinforcers (sweetness) and postingestive reinforcers (nutrients) lead to the same kinds of behavioral change. In the current experiments, weanling rats with oral and gastric cannulas repeatedly experienced a flavor paired with either sweetness, high caloric density, or neither. Rats were then tested for differences in appetitive olfactory orienting and consummatory oral responsiveness elicited by the flavor. Results suggest that oral reinforcement (sweetness) produces conditioning of appetitive responding to the flavor, while postingestive reinforcement produces conditioning of consummatory responding. A second experiment indicates that these behavioral changes are specific increases in responsiveness conditioned by flavor + unconditioned stimulus (US) pairing, and are unlikely to be nonspecific effects of daily unconditioned stimulus exposure.