The CS-US delay gradient in flavor preference conditioning with intragastric carbohydrate infusions.

Rats are able to associate a flavor with the delayed presentation of food, but the obtained flavor preferences are often weak. The present studies evaluated the effect of delay between a flavor CS and a post-oral nutrient US on the expression of conditioned flavor preferences. In Experiment 1, rats were trained with two CS flavors: one was followed after a delay by intragastric infusion of 8% glucose, and the other was followed after the same delay by intragastric water. Rats trained with 2.5, 10, and 30-min delays expressed significant (84-68%) preferences for the glucose-paired flavor whereas rats trained with 60-min delays were indifferent (51%). Experiment 2 examined flavor conditioning over a 60-min delay using 8 or 16% Polycose based on findings that orally consumed Polycose conditions preferences at this delay interval. The 8 and 16% Polycose infusions produced significant preferences which peaked at 62% and 73%, respectively. The ability to bridge these delays may allow animals to learn about slowly digested foods.