Of course the direction of causality for these differences in sensitivity to dopamine is not known. ( 11) used raclopride binding to measure density of D2 receptors and found an inverse relationship between D2 receptor density and BMI. The same is true in obese individuals ( 11). Drug abuse is associated with decreased sensitivity of the dopamine-reward system ( 9). ( 10) demonstrated that the same is true for food. Cocaine use causes release of striatal dopamine and in a raclopride binding study, Small et al. Two of the major players in the reward circuit are dopamine and the endogenous opiates. NeurochemistryĪ study of the neurochemistry of reward provides a great deal of evidence for similarity between food and drug cravings. An unexpected outcome of the study was that a few of the subjects reported craving the beverage during the week in which they returned to baseline eating even though they did not like it. So nutritional deprivation is not necessary to produce food cravings. By the end of the monotony phase of the study, subjects reported that they did not find the beverage to be particularly palatable and there was, indeed, a large increase in frequency of food cravings during this period. The experimental manipulation was to place subjects on a nutritionally adequate but boring and restrictive diet, a vanilla-flavor dietary supplement beverage, for 5 d. The purpose of the study was to determine whether nutritional deprivation was necessary to produce food craving. Although craved foods are generally also liked, there are some examples of a wanting/liking distinction for food as well ( 8). The most commonly cited example of the wanting/liking distinction is that drug addicts report that they continue to crave their drug long after they have stopped enjoying it ( 1). Yet their self-reports were that the stimulation felt strange, not pleasant. The assumption was that the stimulation must be pleasurable, because the patients reported that they felt compelled to continue pressing the button for stimulation ( 7). So these were clearly reward “centers,” but the assumption that wanting and liking were one and the same was so strong that they were frequently called “pleasure centers.” In the 1960s a handful of patients with intractable brain diseases were implanted with such electrodes. In 1954, Olds and Milner ( 6) reported on brain sites that, when electrically stimulated, were extremely rewarding and led to very high rates of bar pressing in rats. Cravings are associated with more snacking and less compliance with dietary restrictions ( 4) and also predict higher BMI ( 5). Binge eating/bulimia have long been associated with food craving ( 3). However, evidence has recently been building that craving and related phenomena do predict intake. So, many question the practical value of understanding desire for a specific food, or craving. Hunger has traditionally been the focus of studies on obesity. strong desire) functional MRI (fMRI) recordings show strong activation of sensory-memory–related brain areas ( 2). Liking and wanting differ from hunger in that they have specific objects of reference. A reasonable working hypothesis is that, going in the other direction, reward enhances desire for and pleasure derived from a stimulus. Pleasure may be rewarding, but other reinforcers such as glucose in the gut may be rewarding without the conscious experience of pleasure. It is often assumed that rewards are pleasurable, but see below for evidence to the contrary. Reward, or reinforcement, has traditionally had a rather circular definition as that which increases the probability of the behavior that precedes it. We take wanting to mean desire and will discuss evidence showing that it is possible to want a stimulus without liking it. Liking is synonymous with pleasantness or the evaluative response to a stimulus. Liking is defined as the hedonic response to a stimulus. Yet there tends to be a great deal of confusion over the definitions of and the relations among these terms. In such discussions, the terms liking, wanting, and reward are frequently used. If food is addictive then other questions arise such as: “Is food then bad for us? Is palatable food particularly bad for us? Should we then outlaw extremely palatable food? Will the obesity epidemic go away if we all stick to gruel?” Drug addicts crave, but do not enjoy, a drug ( 1).
Hippocampus anatomy addiction scholarly articles manual#
Most of the evidence for or against addiction (now called dependency in the Diagnostic and Statistical Manual of Mental Disorders) focuses on similarities and differences between food craving and drug craving. This is a brief review of the concept of food addiction in humans.