Flavor-illness aversions: potentiation of odor by taste in rats

Abstract

For the Sprague–Dawley rat, the odor of almond-scented water proved to be a weak cue for lithium chloride-induced illness, while the taste of saccharin water was very effective. However, when the weak almond color was combined with the strong saccharin taste into a compound cue and followed by lithium chloride-induced illness in a compound conditioning paradigm, taste strongly potentiated odor. Before illness, rats were hesitant (neophobic) to consume almond-scented saccharin solutions. During extinction tests conducted after the compound solution was paired with illness, rats displayed a stronger aversion to the odor component than to the taste component. Aversions for the odor component increased in direct proportion to the concentration of the taste component that was present only on the conditioning trial. Tests with anosmic rats indicated that almond-scented tap water was primarily an olfactory cue having little if any taste component. In contrast, when the almond odor was combined with saccharin taste in a second-order conditioning paradigm, rats did not use odor to avoid taste previously made aversive by illness; nor did they acquire aversions for taste paired with aversive odor. Synergistic potentiation of aversions for the weak stimulus component by the strong component contrasts with the interference effects usually observed in classical conditioning. Taste may index the memory for distal poison cues when toxicosis is delayed after ingesting poison to circumvent interference by intervening cues. This allows the animal to form selectively an aversion for distal poison cues, thus reducing the risk of tasting poison.