Alternating ingestive and aversive consummatory responses suggest a two-dimensional analysis of palatability in rats

The hedonic response to a taste is typically regarded to be the product of a central integration of gustatory afferent information, which ends in a single decision about the nature and intensity of the response to be given. This hedonic response is often characterized as a point lying along a single dimension of palatability, stretching from strongly positive to strongly negative. The present analysis of species-specific consummatory responses suggests that the final response is not made on the basis of a single central analysis of taste information but rather is the result of a competition between two separate systems that are activated by tastes. A single oral infusion of a taste solution may elicit rapid alternation between ingestive and aversive consummatory responses. Such alternation is better interpreted as due to a simultaneous activation of two palatability dimensions than as a reflection of neutral palatability. When increases in the magnitude of aversive responses are produced by taste mixtures, there is not necessarily a reciprocal decrease in ingestive responses. This asymmetry supports the hypothesis of independent palatability dimensions.