Abstract
There is growing evidence that repeated consumption of highly palatable, nutritionally poor “junk food” diets can produce deficits in cognition and behavioral control. We explored whether long-term junk-food diet exposure disrupts rats' ability to make adaptive choices about which foods to pursue based on (1) expected reward value (outcome devaluation test) and (2) cue-evoked reward expectations (Pavlovian-to-instrumental test). Rats were initially food restricted and trained on two distinct response-outcome contingencies (e.g., left press chocolate pellets, and right press sweetened condensed milk) and stimulus-outcome contingencies (e.g., white noise chocolate pellets, and clicker sweetened condensed milk). They were then given 6 weeks of unrestricted access to regular chow alone (controls) or chow and either 1 or 24 h access to junk food per day. Subsequent tests of decision making revealed that rats in both junk-food diet groups were impaired in selecting actions based on either expected food value or the presence of food-paired cues. These data demonstrate that chronic junk food consumption can disrupt the processes underlying adaptive control over food-seeking behavior. We suggest that the resulting dysregulation of food seeking may contribute to overeating and obesity.
Highlights
The global obesity epidemic remains a serious health concern driven in part by changes in the global food supply—more cheap and processed foods are readily available in developed and developing countries than ever before [reviewed in Swinburn et al [1]]
Normal chow-fed rats will inhibit their pursuit of a palatable food reward if they have been given the opportunity to feed to satiety on that particular food prior to testing [17, 18]
Rats given 6 weeks of junk-food exposure tended to disregard the current value of potential foods when engaged in food-seeking behavior, and failed to use cue-elicited food expectations to guide their selection of actions based on the specific foods they produce
Summary
The global obesity epidemic remains a serious health concern driven in part by changes in the global food supply—more cheap and processed foods are readily available in developed and developing countries than ever before [reviewed in Swinburn et al [1]]. Rats that have been maintained on a diet that includes sugary or fatty foods seem to lose this ability to control their food seeking, in that they are more likely to seek out a food upon which they have been sated, relative to controls [14,15,16, 19] Such diets appear to cause behavioral insensitivity to food devaluation regardless of whether that behavior is the product of instrumental [14,15,16] or Pavlovian conditioning [19]. Given evidence for junk food-induced impairments in learning and memory [20,21,22], junk-food diets may interfere with more cognitive aspects of behavioral control, such as the ability to retrieve and make use of specific action-outcome or stimulus-outcome mappings. This latter hypothesis predicts that junk-food diets should impair control over specific food-seeking actions even when food values are not the primary basis for decision-making
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