Hunger enhances the expression of calorie- but not taste-mediated conditioned flavor preferences

Rats learned to associate one flavor conditioned stimulus (CS; grape or orange) with an ethanol (caloric) or saccharin (sweet but noncaloric) solution unconditioned stimulus (US), and the other flavor CS with either the other US or plain tap water. They were then given two-bottle choice tests between the flavor CSs apart from the USs. Flavors associated with 5% ethanol were preferred over saccharin-paired and water-paired flavors by sated rats, and food deprivation during the choice test enhanced this preference. The ethanol-paired flavor preference was not affected by feeding conditions (deprived vs. ad lib) during CS-US conditioning. Flavors associated with 8% sucrose (caloric + sweet tasting) were preferred over water-paired flavors during ad lib testing, and this preferences was also enhanced by food deprivation. Flavors associated with 0.028% or 0.25% saccharin were preferred over flavors paired with water; however, these preferences were not enhanced by deprivation at test time. In all cases, calorie-mediated preferences, at their highest levels, were stronger than taste-mediated preferences. These experiments indicate that preferences for flavors associated with caloric substances are positively related to hunger level at test time, but preferences mediated by a prior preferred taste are independent of test-time hunger level.