Journal of Experimental Psychology: Copyright 2000 by the American Psychological Association, Inc. Animal Behavior Processes 0097-7403100/$5.00 DOI: 10.1037//0097-7403.26.1.15 20G0, ~,bl. 26, No. I, 15-30 Motivational State Regulates the Content of Learned Flavor Preferences Justin A. Harris, Marika C. Gorissen, Glynis K. Bailey, and R. Frederick Westbrook University of New South Wales Rats acquired a preference for an aqueous odor (almond) presented in simultaneous compound with sucrose. Separate presentations of saccharin reduced this preference in rats with ad-lib access to food during training or at test, but not in rats that were hungry during both training and test. In contrast, separate presentations of sucrose reduced the preference for the almond irrespective of deprivation state during training and test. We interpret the results to mean that a hungry rat forms odor-taste and odor-calorie associations, and its motivational state on test determines which of these associations controls the preference. In contrast, a rat that is not hungry during training only forms an odor-taste association, and its performance on test is independent of its level of hunger. When an animal consumes a novel substance, it learns about the simultaneous relations among the flavor compo- nents (odors and tastes) of the substance and about the association between those components and their postinges- five consequences (nutritional gain or illness). Both types of association contribute to acquired preferences for foods (Capaldi, 1996; Sclafani, 1997). For example, if rats are exposed to a solution composed of an aqueous odor in simultaneous compound with saccharin, they will subse- quently show a clear preference for a solution containing the odor alone (Fanselow & Birk, 1982; Holman, 1975). Be- cause saccharin has no nutritional value, one can infer that the association between the odor and the sweet taste was solely responsible for the conditioned odor preference. The clearest evidence that learned preferences can be mediated by an association with calories comes from demonstrations that rats acquire preferences for odors or tastes that have been paired with intragastric infusions of sugar or starch (Azzara & Sclafani, 1998; Sclafani & Nissenbaum, 1988) or with injections of glucose directly into the portal vein (Tordoff & Friedman, 1986). One very popular and robust paradigm for investigating conditioned flavor preferences involves exposing rats to a simultaneous compound composed of an aqueous odor and sucrose (e.g., Capaldi & Myers, 1982; Capaidi, Myers, Campbell, & Sbeffer, 1983; Mehiel & Bolles, 1984, 1988a, 1988b). Sucrose has both an attractive (sweet) taste and contains calories, and thus the acquired odor preferences Justin A. Harris, Marika C. Gorissen, Glynis K. Bailey, and R. Frederick Westbrook, School of Psychology, University of New South Wales, Sydney, Australia. We thank Bob Boakes and Rick Richardson for their comments. This research was supported by Grant A79600566 from the Australian Research Council, and all procedures have been ap- proved by the Animal Care and Ethics Committee at the University of New South Wales. Correspondence concerning this article should be addressed to R. Frederick Westbrook, School of Psychology, University of New South Wales, Sydney, Australia 2052. Electronic mail may be sent to f.westbrook @unsw.edu.au. may be mediated by an association between the odor conditioned stimulus (CS) and the sweet-taste uncondi- tioned stimulus (US) or by an association between the odor CS and the calories US. However, it is not clear whether rats do acquire both odor-taste and odor-calorie associations when presented with an odor-sucrose compound, or whether both associations contribute to expression of the odor preference. Several studies have provided evidence that the formation and expression of odor-taste versus odor-calorie associations are regulated by the rats' levels of hunger. For instance, Fedorchak and Bolles (1987) exposed hungry rats to a simultaneous compound composed of either an odor and sucrose or an odor and saccharin. They found that the rats' preferences for the odor associate of sucrose was greater if the rats were tested hungry than if they were tested with ad-lib access to food, but there was no such differential effect of hunger at test on the rats' preferences for the odor associate of saccharin. Capaldi, Owens, and Palmer (1994) extended these findings by showing that preferences for an odor associate of sucrose, but not for an odor associate of saccharin, was greater if the rats were food deprived during training than if trained with ad-lib access to food. Thus, making rats hungry during training and test reveals a dissociation between the preference conditioned with su- crose versus that conditioned with saccharin. This suggests that rats exposed to an odor-sucrose compound form an association between the odor and calories and that this association contributes to their odor preference. Further, these findings indicate that hunger regulates both the forma- tion and expression of the odor-calorie association, presum- ably by enhancing the value of calories. These demonstrations provide strong evidence that the preference shown by hungry rats for an odor associate of sucrose involves an association between that odor and calories. However, they do not indicate whether the associa- tion between the odor and the taste of sucrose contributes to the odor preference among hungry rats, nor do they indicate whether the association between the odor and calories contributes to the conditioned preference shown by sated rats. Indeed, even the evidence that calories contribute to the preference among hungry rats does not establish that the 15