Caffeine-reinforced conditioned flavor preferences in rats

In 4 experiments, rats were trained to associate 1 of 2 differently flavored solutions with caffeine. During later 2-bottle extinction tests, they consistently preferred flavors that had been previously mixed with 2 lower (0.25 and 0.125 mg/ml), but not 2 higher (0.5 and 0.75 mg/ml), caffeine concentrations. Hunger during conditioning increased the size of these preferences, but neither preexposure to unflavored caffeine nor hunger during the choice test had any effect on them. Because caffeine is noncaloric, this last finding strengthens the hypothesis that hunger enhances the expression of only calorie-based conditioned flavor preferences. More fundamentally, the present results represent the first clear evidence that, through Pavlovian conditioning, rats can develop preferences for flavors associated with caffeine.