You all may remember that Sci's recent posts have focused on eating, overeating, and dopamine. Today, Sci continues this trend. Honestly, she couldn't stop thinking about it. How is overeating like addiction? How is it different? And so she began to look up a bunch of papers on binge eating and dopamine.
I was particularly interesting in the changes in food intake and reward associated responses in people with eating disorders like bulimia nervosa and anorexia nervosa. There are many hypotheses as to why these eating disorders exist, ranging from problems with society (which can certainly contribute to the incidence of the disorders), to hypotheses of obsessive control akin to the compulsions seen with OCD, to increased sensitivity to reward, to decreased sensitivity to reward.
This increased/decreased sensitivity to reward (some people have seen decreased sensitivity to reward in rats, along with increased self-administration of pleasurable things, but what this actually translates to in humans can be difficult to interpret) was particularly interesting, and so Sci was very glad when she came across this study.
Schienle et al. "Binge-Eating Disorder: Reward Sensitivity and Brain Activation to Images of Food ", Biological Psychiatry, 2008.
Sci finds it very interesting that in her Pubmed searches for bulimia and dopamine related stuff, almost all of the papers she found related to binge-eating, but not exclusively to bulimia. Upon reflection, this isn't so surprising. After all, bulimia nervosa can be broken down into two components: the binge portion and the purge portion. The binge portion is similar if you have bulimia nervosa or is you are a binge eater, while the purge portion is specific to people with bulimia, and so if you wanted to study bulimia (especially in related to reward-related stimuli) it would make sense to study the binge-eating portion of it, and thus to study binge eating without also studying purging. In addition, the purging portion of bulimia nervosa can take many forms, including diet, drug taking (like laxatives or diet drugs), excessive exercise, and vomiting.
But binging really only takes one form, whether it's in people with bulimia, or people with binge eating disorder (BED): the consumption of high amounts of palatable food, usually high in sugar or fat (or both). Binging is often brought on by negative stimuli (depression, loneliness, etc) in both people who binge eat and in people with bulimia nervosa), which means that binge eating and the binging in anorexia may be similar. Finally, when you're going to study reward related mechanisms, you would probably want to study binging as separate from purging, as purging is less directly related to reward mechanisms (if it is related to reward mechanisms at all).
So anyway, this study set out to look at how people who binge eat react to food stimuli relative to non-binge eating controls. They took a bunch of women, some overweight binge eaters, some normal weight with bulimia nervosa, and two control groups of overweight non-binge eaters and normal weight non-bulimic women. Sci was very pleased that they used women in this study, bulimia nervosa is far more prevalent among women than men, and also it galls her that lots of studies use only male patients (or rats, or mice, or monkeys) for anything not directly requiring a uterus. Many humans studies at this point have had to branch out into both males and females to make sure they get enough participants, and this is a really good thing, Sci thinks. Anyway.
They took these four groups of women, made them fast overnight for 12 hours, and stuck them in an MRI. They then showed them pictures of delicious foods (in the methods it says they used french fries, ice cream, cake, and chips) as well as pictures of things that were disgusting (like maggots) and things that are neutral (like a mop). Of course, since all of the patients had fasted for 12 hours, they thought all the good looking food looked very tasty indeed, and all groups equally thought the maggots were gross and the mop was boring. And then they looked at the patients' brains. And this is what they got:
(Interpretations aside, one cannot help but note that MRI makes for very pretty pictures)
So what on earth are you looking at? What you're looking at is a series of averaged brain scans in the four groups of patients (from left to right, you have Binge eating, Bulimic, normal weight controls, and overweight controls). You're looking at an axial slice, which hear shows a brain sliced through the middle as a hamburger bun is sliced.
Not surprisingly, certain parts of the brain (which you can see) were activated in all the participants when viewing tasty cakes. Lots of areas associated with rewarding aspects of stimuli lit up, including the nucleus accumbens (increases in the neurotransmitter dopamine in this area area related to the reward associated effects of things like food and drugs like cocaine) and the striatum. Areas also lit up associated with arousal (of course you would be aroused (not like THAT, you pervert, I mean awake or attentive to) by tasty food when you're hungry) including the amygdala. In addition, other areas, including the insula and medial orbitofrontal cortex, lit up. The insula is everyone's new pet brain area, and is thought to be involved in signal processing and reward processing, and the orbitofrontal cortex is thought to be involved in things like processing of complex stimuli and decision making.
And there were some interesting differences between the groups. Though all the groups lit up the same brain areas, the binge eating group and the bulimic group lit up in some areas more than others. The binge eating group showed a greater response in the orbitofrontal cortex than anyone else, while the bulimic group showed a greater response in the nucleus accumbens and insula. The binge eating and bulimic group also both showed higher arousal correlated with the activity in these brain areas than the control groups did.
So what do these things mean?
Well, the insula activation was expected, it's involved in the "gustatory" cortex of the brain, related to taste in particular, and so would respond to things that we perceive to be tasty (like cake). What is interesting is that people with bulimia may (due to increased activation of this area) perceive tasty things as even MORE tasty than people who are not bulimic. The orbitofrontal cortex is also involved in gustatory processing, and so increased activation in this area among binge eaters might mean that they perceive tasty foods as being tastier than people who do not binge eat.
The authors concluded that people who binge eat and people who are bulimic both are more sensitive to food reward than those who do not binge eat at all. This is an interesting finding to Sci for a couple of reasons. At first sight it might seem weird, if we are trying to relate severe binge eating to an addiction. After all, addicts are usually tolerant to the effects of their drug (which is why they have to take more), and animal studies show some reward-related tolerance after binge eating, though it depends on the study. But this study is not showing the reward-related effects of tasty food directly in these patients, because the patients aren't EATING. Instead, they are looking at tasty food, which is something that might stimulate craving. Comparing an increased reward-related response in binge eaters to similar results seen in drug craving makes a lot of sense to Sci. It would be REALLY cool to see how they compared in an MRI if you gave them the food, how they would respond, and whether the responses are blunted, like those seen in studies with drug addicts (Sci looked for this study, and it appears it hasn't been done, but Sci doesn't buy that...anyone?).
The increased response in the nucleus accumbens in bulimic patients is also interesting. The authors thing that this is due to the increased attention that these patients are paying to the reward-related stimuli, in this case the food. Sci thinks it might also be worth looking into the way that these patients EXPECT the food to taste (say on a scale of "good" to "incredibly freakin' awesome"). Accumbens activity (and the dopamine signaling there in particular) may have some relation to the reward we have come to expect, rather than the "goodness" of the reward itself, and so this could tell us more about whether the increased signals seen in the MRI in bulimic patients correspond to the actual feeling of increased sensitivity to the "goodness" of the food.
So what's the take home message here? The take home message is that people who binge eat, whether bulimic or binge eaters, appear to respond more intensely to food than controls. Interestingly, binge eaters respond more intensely in one area, while bulimics respond more intensely in another. Sci thinks this is REALLY interesting, and she has no idea WHY this could be the case. It could be that this is a really important difference between binge eaters and people with bulimia nervosa. Obviously, we're just going to have to do more science to find out.
Sci has to finish this post out with a couple of points:
1) This is an fMRI study. While these studies are really useful for correlations of brain activity with things (like pictures of food), they can't really tell us WHAT that activity is actually doing. Each brain area you're looking at is composed of tons of neurons of many different types. We know that blood flow and oxygen is going there (that's what fMRI measures), but what cells are firing in response? Where are those neurons that are firing projecting TO? With what neurotransmitters are they firing and what impact are those neurotransmitters having elsewhere in the brain??
These are all questions that fMRI can't answer. fMRI is a great tool for looking in humans, looking at complicated stimuli, and looking for correlations. But it's not a great tool for telling us precisely what is happening in what areas of the brain, and where those areas are having effects. For that, you need more detailed studies in animals, where you can actually look into the brain to see what's going on, where, and when. Then, when we someday have a really good picture, we can go back to the MRI, and put some puzzle pieces together.
2) If you are a binge eater, or someone with bulimia nervosa, or think you might be, PLEASE seek help. This is not a matter of being "weak-willed" or anything, it's a matter of psychiatry, your neurochemistry, and your health. Sci has seen several people in her life fall victim to disorders like these, and they are truly heart-breaking for everyone involved. So seek help. There is the National Association of Anorexia Nervosa and Associated Eating Disorders (ANAD) helpline at 630-577-1330, and there is also the Overeaters Anonymous (OA) helpline at 505-891-2664.
Schienle, A., Schäfer, A., Hermann, A., & Vaitl, D. (2009). Binge-Eating Disorder: Reward Sensitivity and Brain Activation to Images of Food Biological Psychiatry, 65 (8), 654-661 DOI: 10.1016/j.biopsych.2008.09.028