Control of fluid palatability by exteroceptive Pavlovian signals

Tastes elicit a set of palatability-dependent orofacial and somatic responses in rats. We investigated whether discrete auditory conditioned stimuli that signal the availability or onset of unconditioned taste stimuli (sucrose, quinine) can control orofacial responses in the absence of those unconditioned stimuli. In Experiment 1, one auditory stimulus (CS+) was paired with the delivery of a sucrose solution to the magazine floor, and another auditory stimulus (CS-) was never followed by sucrose. Following conditioning, oral infusions of water that were preceded by the CS+ were found to elicit more ingestive (sucrose-typical) orofacial responses than did water alone or water preceded by the CS-. In Experiment 2, the conditioned ingestive reactions to a signal for sucrose observed in Experiment 1 again occurred, and conditioned aversive (quinine-typical) orofacial responses occurred in response to water infusions preceded by a former signal for quinine. These data suggest that perceived palatability may be influenced by Pavlovian associations involving exteroceptive conditioned stimuli. Further, they illustrate the importance of supporting stimuli in modulating the effects of Pavlovian associations upon behavior.