Overlapping Neural Correlates for Food and Drug Research Paper

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Overlapping Neural Correlates for Food and Drug Addiction

Food Addiction

The Neural Correlates of Food and Drug Addiction Overlap

A recent popular press article in the Huffington Post reviewed a recently published research article that revealed the brain functions in a similar manner whether a person is addicted to food or drugs. Women scoring high as emotional eaters and exposed to a milkshake preferentially activated the anterior cingulate cortex, medial orbitofrontal cortex, dorsolateral prefrontal cortex, amygdala, and caudate, as imaged by fMRI. The lateral orbitofrontal cortex was less active when compared to the brains of subjects scoring low as emotional eaters. These areas correspond to those that have been found to be involved in drug using/seeking behavior, which suggests the mechanisms involved in food and drug addiction are similar or the same. Previously published research studies support this conclusion, although addiction-related behaviors are very complex and additional studies will be required to further elaborate the significance of the findings.

Introduction

An article published this past week in the Huffington Post (2011) reviewed a recently published research study (Gearhardt et al., 2011) that revealed an overlap between brain activity patterns related to compulsive eating and drug addiction. Brain activity patterns, as monitored through positron emission tomography (PET) or functional magnetic resonance imaging (fMRI), has long been used to locate parts of the brain involved in executing a specific behavior. A number of studies have localized those areas of the brain that are more active when a cocaine addict, for example, is exposed to drug cues. The research study reviewed here took a similar approach and localized areas of the brain believed to be involved in emotional eating. What was unexpected was how closely the brain patterns involved in food addiction match those found to be involved in drug seeking behaviors, a finding that suggests important overlaps between the two disorders that may have implications in how obesity will be treated and prevented in the future.

Methodology

A total of 48 young women (mean age = 20.8) with levels of obesity ranging from lean to morbidly obese (BMI range = 23.8-39.2) were enrolled in the study. Women suffering from binge eating or anorexia/bulimia, drug addictions, a recent brain injury, or currently using psychotropic medications were excluded from the study. The women were then offered either a tasty milkshake or artificial saliva (control), while their brain activity was monitored by fMRI. Artificial saliva was used instead of plain water to avoid stimulating the taste senses.

The independent variable was the score each woman obtained on an instrument designed to measure a tendency for addictive behaviors (YFAS). High YFAS scores correlated with both emotional eating and external eating high scores as determined by the Dutch Eating Behavior Questionnaire.

Results

The areas of the brain that were preferentially activated in women scoring high in emotional/external eating and shown a picture of a milkshake were the anterior cingulate cortex, medial orbitofrontal cortex, and the amygdala. Being offered an actual milkshake activated the dorsolateral prefrontal cortex and caudate in these women, but when the food was actually handed to them less activity was observed in the lateral orbitofrontal cortex. The level of obesity or age was not a reliable predictor of brain activity patterns in this study.

Discussion

One of the remarkable aspects of this study is the statistical strength of the findings given the low sample size. This argues in favor of the value and sensitivity of the YFAS instrument in assessing addictive eating tendencies and predicting which brain areas are likely to be involved in this behavior. On the negative side, the small sample size precluded further elaboration of the findings relative to a number of potential confounding factors (discussed below). Other variables that could be important include affect, food restriction, gender, age, stress, and genetics (reviewed by Mathes, Brownley, Mo, and Bulik, 2009).

Binge eating is considered a form of food addiction and the main factors contributing to binge eating is a history of highly-palatable food restriction, stress, and the availability of palatable foods, as defined by both animal and human studies (Mathes et al., 2009). The subjects studied by Gearhardt et al. (2011) were not food restricted or reportedly stressed, but a subset did score high in emotional/compulsive eating that could be the result of a history of compulsive eating. A single exposure to their drug of choice will often induce drug addicts to relapse. This type of behavior is believed to be equivalent to the behavioral effects of food restriction (reviewed by Mathes et al., 2009).

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Rodents having a history of prolonged intermittent exposure to sugar solutions behave in a manner that replicates drug seeking/using behavior in humans, and experience similar neurobiological changes. Symptoms of withdrawal are also observed. These findings, as reviewed by Mathes et al. (2009), lend considerable independent support for the concluding that food addiction may depend on the same or similar brain areas as those involved in drug addiction.

An fMRI study comparing brain activities between regular and compulsive eaters, who were matched by level of obesity, revealed significant differences in brain areas activated under conditions of hunger, anticipation, and reward (Coletta et al., 2009). The compulsive eaters preferentially activated several brain areas, including the dorsolateral prefrontal cortex. In contrast, regular eaters experienced increased activation in the orbitofrontal cortex and left dorsolateral prefrontal cortex. These results were interpreted as indicating that fasted compulsive eaters were hungrier when shown palatable food and regular eaters enjoyed the meal more when fed. These could help explain why the emotional eaters in the Gearhardt et al. (2011) study also activated the dorsolateral prefrontal cortex, an area of the brain believed to be involved in managing the symptoms of craving, withdrawal, motivation, expectancy, and drug seeking behavior in drug addicts (reviewed by Gearhardt et al., 2011). There were many differences in brain activity patterns between these two studies as well, which suggests the neural correlates of food addiction are still incompletely understood.

A comparison of brain activity patterns between randomly-assigned college students maintained on either a monotonous or regular diet, was sufficient to reveal difference in brain activity when the subjects simply imagined a monotonous diet or their favorite foods (Pelchat, Johnson, Chan, Valdez, and Ragland, 2004). Of the brain areas preferentially activated in subjects maintained on a monotonous diet, the caudate, amygdala, anterior cingulate cortex overlap with the results of Gearhardt et al. (2011). In drug addicts the caudate has been linked to expectations of positive rewards, high value incentives, and exposure to drug cues (reviewed by Gearhardt et al., 20110). The amygdala has been linked to high-value food feeding motivation, while the anterior cingulate cortex has been found to have a reduced dopamine receptor density in alcoholics at risk for relapse. Pelchat et al. (2004) interpreted their findings as supporting a role in food craving and/or food liking, an interpretation consistent with the findings by Gearhardt et al. (2011).

A person's mood has a powerful modifying effect on brain activity when confronted with low or high calorie food (Killgore and Yurgelun-Todd, 2006). In women judged to have a positive affect when presented with a high calorie food, their lateral orbitofrontal cortex was preferentially activated during fMRI imaging studies. When presented with a low calorie food the medial orbitofrontal cortex was activated. Women judged to have a negative affect had the opposite brain activity pattern to the two food groups. A negative affect would therefore predispose an individual to choosing a high calorie food (unhealthy) over a low calorie food (healthy), since activation of the lateral orbitofrontal cortex has been associated with resisting temptation. Gearhardt et al. (2011) likewise found lower activity in the lateral orbitofrontal cortex in subjects with a high emotional eating score, a result that may indicate an inability to resist highly palatable foods when suffering from either compulsive eating habits or a bad mood.

PET scans of cocaine addicted individuals revealed elevated dopamine release from the dorsal striatum (includes the caudate) when viewing a video of people using cocaine, but not when viewing a video lacking drug cues (Volkow, 2006). A positive correlation was found to exist between cocaine users scoring highest in terms of withdrawal symptoms and the largest increase in dopamine production from the dorsal striatum (Volkow, 2006). This finding is consistent with those by Gearhardt et al. (2011) that revealed emotional eaters had the highest caudate activity when shown a picture of a milkshake.

Summary

The findings of Gearhardt et al. (2011) are generally supported by other fMRI studies investigating abnormal eating behaviors, although the degree of overlap in brain patterns between the studies discussed here was incomplete. The Gearhardt et al. (2011) experimental design was simple and straightforward, which precluded delineating the effects of a number of potential confounding factors such as hunger, stress, and a subject's emotional state. There is also sufficient evidence to support the theory by Gearhardt et al. (2011) that food and drug addiction utilize similar brain pathways and suggests eating disorders involving food.....

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