Dopamine and food addiction: lexicon badly needed

Abstract

Over the last few years, the concept of food addiction has become a common feature in the scientific literature, as well as the popular press. Nevertheless, the use of the term addiction to describe pathological aspects of food intake in humans remains controversial, and even among those who affirm the validity of the concept, there is considerable disagreement about its utility for explaining the increasing prevalence of obesity throughout much of the world. An examination of the literature on food addiction indicates that mesolimbic and nigrostriatal dopamine systems often are cited as mechanisms that contribute to the establishment of food addiction. However, in reviewing this literature, it is important to have a detailed consideration of the complex nature of dopaminergic involvement in motivational processes. For example, although it is often stated that mesolimbic dopamine mediates reward, there is no standard or consistent technical meaning of this term. Moreover, there is a persistent tendency to link dopamine transmission with pleasure or hedonia, as opposed to other aspects of motivation or learning. The present article provides a critical discussion of some aspects of the food addiction literature, viewed through the lens of recent findings and current theoretical views of dopaminergic involvement in food motivation. Furthermore, compulsive food intake and binge eating will be considered from an evolutionary perspective, in terms of the motivational subsystems that are involved in adaptive patterns of food consumption and seeking behaviors and a consideration of how these could be altered in pathological conditions.

Figure 1

For several years, researchers have been making distinctions between aspects of motivated behavior that are differentially affected by dopaminergic manipulations. Salamone (82) emphasized the distinction between directional aspects of motivation (i.e., that behavior is directed towards or away from stimuli) and activational aspects of motivation (i.e., that motivated by behavior is characterized by a high degree of activity, vigor and persistence), and suggested that DA antagonists impair activational aspects of food motivation but leave directional aspects intact. Blackburn et al. (135) suggested that DA antagonists impaired preparatory behaviors instigated by a conditioned stimulus at doses that did not impair consummatory behavior. Salamone (96) emphasized the distinction between consummatory behaviors and instrumental responses, and also tried to link this distinction to others by stating that highly active instrumental behaviors elicited and supported by conditioned stimuli are very sensitive to disruption of accumbens DA transmission. Berridge (34) distinguished between the role of DA in “liking” vs. “wanting”, and suggested that interference with striatal and accumbens DA transmission affected incentive motivation (“wanting”) for sucrose, but had little effect on hedonic reactions instigated by sucrose (“liking”). Foltin (136) distinguished between food “seeking” (i.e., instrumental responses reinforced by food) vs. “taking” (consumption), and reported that amphetamine increased food seeking behavior while decreasing food taking behavior. More recently, Ikemoto and Panksepp (137) and Burgdorf and Panksepp (138) stated that it is useful to distinguish between consummatory “reward”, which is relatively unaffected by interference with accumbens DA transmission, and preparatory or anticipatory aspects of “reward”, which are more greatly impaired. Czakowski et al. (139) studied the effects of DA antagonism on ethanol seeking and intake, and reported that the D2 antagonist remoxipride had substantial effects on measures of ethanol seeking behavior (lever pressing) in a dose range that had little effect on ethanol intake.