G. B. Shaw: " There is no sincerer love than the love of food”

The regulation of food intake by the central nervous system is controlled by a complex interplay of various brain circuits. For instance, the so-called brain reward system responds to environmental stimuli learned through classical conditioning, which signal the imminent availability of an attractive food. Thus, advertising logos of well-known fast-food chains can serve as powerful stimuli. Unexpectedly, the brain reward system responds to such conditioned stimuli in the environment even under satiety. In rodent studies, it was found that the mere presentation of a conditioned tone stimulus predictive of palatable food can reinitiate food intake in a fully satiated laboratory mouse. Therefore, conditioned stimuli associated with attractive food can stimulate food intake even without physiological need, e.g. under satiety, a mechanism that could promote overweight and obesity. Our current work has tested this assumption in detail . Specifically, we tested laboratory rodents in a complex paradigm ("Pavlovian-instrumental transfer task"). Using this task, we measured the extent to which Pavlovian food-predictive stimuli can invigorate lever pressing for food: the higher the number of lever presses, the higher the stimulus-induced food-related motivation. Laboratory rodents were studied under mild food deprivation vs. satiation. Satiation was induced by short term pre-feeding before test or by pharmacological blockade of a hunger hormone. Data revealed that, invigoration of lever pressing by Pavlovian stimuli was massively reduced under satiety as compared with mild hunger. However, the role of a key structure of the reward system, the nucleus accumbens, in mediating this effect could not be clarified. Overall, our results are not consistent with the notion that conditioned, food-predictive stimuli can act on the brain reward system to initiate food-related responding even under satiety. Thus, the interaction of those brain circuits that process learned stimuli in the environment signaling palatable food, as well as those that trigger the trip to the next restaurant and control the number of courses to be ordered, is more complex than originally assumed.