Food-associated Cues Research Articles

Amygdala subsystems and control of feeding behavior by learned cues.

A combination of behavioral studies and a neural systems analysis approach has proven fruitful in defining the role of the amygdala complex and associated circuits in fear conditioning. The evidence presented in this chapter suggests that this approach is also informative in the study of other adaptive functions that involve the amygdala. In this chapter we present a novel model to study learning in an appetitive context. Furthermore, we demonstrate that long-recognized connections between the amygdala and the hypothalamus play a crucial role in allowing learning to modulate feeding behavior. In the first part we describe a behavioral model for motivational learning. In this model a cue that acquires motivational properties through pairings with food delivery when an animal is hungry can override satiety and promote eating in sated rats. Next, we present evidence that a specific amygdala subsystem (basolateral area) is responsible for allowing such learned cues to control eating (override satiety and promote eating in sated rats). We also show that basolateral amygdala mediates these actions via connectivity with the lateral hypothalamus. Lastly, we present evidence that the amygdalohypothalamic system is specific for the control of eating by learned motivational cues, as it does not mediate another function that depends on intact basolateral amygdala, namely, the ability of a conditioned cue to support new learning based on its acquired value. Knowledge about neural systems through which food-associated cues specifically control feeding behavior provides a defined model for the study of learning. In addition, this model may be informative for understanding mechanisms of maladaptive aspects of learned control of eating that contribute to eating disorders and more moderate forms of overeating.

Amygdalo-Hypothalamic Circuit Allows Learned Cues to Override Satiety and Promote Eating

Organisms eat not only in a response to signals related to energy balance. Eating also occurs in response to "extrinsic," or environmental, signals, including learned cues. Such cues can modify feeding based on motivational value acquired through association with either rewarding or aversive events. We provide evidence that a specific brain system, involving connections between basolateral amygdala and the lateral hypothalamus, is crucial for allowing learned cues (signals that were paired with food delivery when the animal was hungry) to override satiety and promote eating in sated rats. In an assessment of second-order conditioning, we also found that disconnection of this circuitry had no effect on the ability of a conditioned cue to support new learning. Knowledge about neural systems through which food-associated cues specifically control feeding behavior provides a defined model for the study of learning that may be informative for understanding mechanisms that contribute to eating disorders and more moderate forms of overeating.

Intake of greasy diets in hypothalamic obesity: a re-assessment

Rats with medial hypothalamic lesions are known to prefer greasy diets. Past research has suggested that this is based on the oily texture rather than caloric content of these foods. We have re-examined this appetite in rats with bilateral parasagittal knife-cuts between the medial and lateral hypothalamus. Following knife cuts vs. sham surgery, the body weight and food consumption of adult female rats were monitored during four experimental phases. During the first month post-surgery rats were fed powdered Chow (3.61kcal/g) and showed the usual hyperphagia and obesity. Each group was then subdivided and fed either a high-fat diet (5.5kcal/g) or a similarly greasy mineral-oil diet (3.61kcal/g) for a second month. The knife-cut group fed high-fat showed significantly higher intake than both sham-cut controls and knife-cut rats fed the mineral-oil diet. The latter group showed only a non-significant feeding increase over controls. Following a third month when all groups again received Chow, animals were given the opposite greasy diet for a final month. Knife-cut rats previously fed the high-fat diet showed significant overeating of the mineral-oil diet and defended their obesity, while those fed the mineral-oil free diet first now showed significant hyperphagia and obesity on the high-fat diet. Across both target phases (months 2 and 4) knife-cut rats always ate significantly more of the high-fat diet than of the mineral-oil diet. The latter only elicited hyperphagia in animals that had been previously exposed to the high-fat diet. These findings suggest that the hyperphagic response to greasy foods relatively low in calories and digestible fats by rats with hypothalamic injury is a function of prior experience with the sensory and/or metabolic consequences of having first eaten highly caloric fatty foods. If that is true, it may be that such animals are capable of learning positive food-associated cues in addition to negative ones (i.e. enhanced taste aversions) documented earlier by other investigators.