This months Hard Science article tackles a problem that has reached epidemic proportions in western society – binge eating and the brain science underlying obesity. Earlier this year Kessler et al. published an exceptionally thorough review article on the neurobiological basis of binge-eating disorder. I was excited when I dug this one up, but my enthusiasm quickly faded as I got lost in a sea of findings from neuroscience, genetic and heritability, and cognitive studies. What I thought would be a quick review of the latest findings turned out to be a slog through some of the most confusing brain research currently available. However, the reading and re-reading was worth the effort, because thanks to this team’s hard work sifting through a massive literature there emerges some consistent facts that point to some exciting possibilities not just for understanding the mechanics of binge eating, but for treating the problem effectively. In the end, Kessler et al. manage to take an ocean of data and distill it into some key points. Essentially, they conclude that people who binge eat “have greater cognitive attentional biases towards food, decreased reward sensitivities, and altered brain activation in regions associated with impulsivity and compulsivity.”
If we put all of the research underlying these key points together, we can set the stage for understanding how understanding how the balance and flow of information and activity in the brain – its functional connectivity – can explain some of the features of binge eating. Let’s begin by summarizing these influences: if you have binge eating disorder, you may have inherited a tendency to think and behave in particular ways thanks to your genetic history. Combine this with your experiences and learning through your life, and it is quite possible that you may not be particularly good at recognizing the source of all your inner sensations and feelings, which could put you at risk of getting hooked on eating to make yourself feel better. You may have developed a pretty strong bias to notice and think about food all the time, and may be prone to compulsively eat instead of finding other solutions to how you are feeling. Food may be a weak area for you in terms of your self-control, even at the best of times, so instead of learning to stop doing this, you have unwittingly learned to do it more.
In terms of brain connectivity, the situation with binge eating looks a lot like most other addictive behaviours. The most prominent systems that are involved are often referred to as the Reward and Executive Circuits. By exploring each of these circuits it is possible to see many of the causes of binge eating in action.
The reward circuit is a collection of brain areas that appear to function together as a sort of network. It is particularly active and involved when it comes to our appetite for food. A central part of the reward circuit is the midbrain (including the ventral tegmental area) and ventral striatum. Activity here is associated with craving and seeking behavior. The Ventral Tegmental Area is stimulated by rewards into releasing dopamine (a feel good, excitatory neurotransmitter) to various parts of the brain including the amygdala (where we experience pleasurable and painful feelings), and the orbitofrontal cortex, which also plays an important role in the functioning of the executive circuit. The orbitofrontal cortex is closely linked to the ventral striatum, and together they are involved in controlling impulses, learning from experience, and directing behavior towards goals. All of these parts are connected by tracts of fibers that make sure that rewards like bingeing quickly get noticed and direct our attention and behavior to getting more food. In normal eaters, this reward system helps people enjoy a meal but also ensures that there is a balance between eating and other pleasures. With binge eating the reward system has become sensitized to food. This increases your appetite and craving so that you will think about, dream about, desire, and want food more intensely and more often than most people. To make matters worse, because the reward network is awash in dopamine from all the food you are consuming, it will dial down its response to eating. In other words, not only do you crave eating, you will need to consume more in order to get an effect from the food you take in.
Executive circuits heavily involve frontal cortex in the brain and overlap with the reward system. The primary executive network is usually associated with three prominent areas in the frontal portion of the brain. The first of these is the dorsolateral prefrontal cortex, which contributes to planning, inhibiting responses, accessing working memory, organizing, reasoning and problem solving. Then there is the anterior cingulate cortex, which is involved in decision-making and motivation. Finally, and overlapping with the reward circuit, there is the orbitofrontal cortex, which plays an important role in maintaining our “filters”. It helps you maintain your focus on a task, gauge whether your behaviour is appropriate to the situation or people you are involved with, and assess risk based on rewards and punishments.
In a healthy person, the reward system functions very predictably, and it co-operates with the executive network by exchanging experience and information so that we control our harmful impulses, engage in successful, goal-directed behaviour, and get the most short term pleasure while ensuring the least long term pain. With binge eating disorder, these systems are disrupted. When you binge the reward system is hijacked into focusing most of its energy on seeking food. Food cues become your primary interest. Food gets most of your attention and your appetite is biased towards seeking it out all of the time. This comes at the expense of all the other things that deserve your attention. The flow of information gets dysfunctional in some very predictable ways. For example, parts of the orbitofrontal and prefrontal cortex, as well as cingulate cortex, drop out of use and result in poorer decision making, less inhibitory control around eating, and biased reward prediction. The usual flow of information in the executive circuit is dysregulated, which translates into bias, oversight, neglect, poor planning, impulsive behavior, and overall poor management of your coping choices. Taken together, this explains most of the problems that you will experience when you have binge eating disorder.
What happens when you get effective treatment or do what is required to stop the binge eating? As is typical of review articles, Kessler et al. don’t touch on this much, and when they do allude to treatment in their discussion they focus exclusively on the possibility that all this neuroscience will spawn new and revolutionary pharmaceutical agents. Like the vast majority of researchers whose heads are buried in the sands of neuroscience, they equate physiological explanations of a problem with treatment using high tech drugs and genetic tinkering. Clinical practice guidelines suggest that these sorts of treatments are pretty useless, whereas there is a rich history of cognitive and behavioural interventions that not only make sense from a neuroscience point of view – they work!
Essentially, for therapy to be effective, the imbalances present in brain activity must slowly get worked out, with functional connectivity and activity returning to the executive circuit and a less sensitivity evident in the reward circuit. How is this done? Most effective treatments will have to result in adjustments to the way information flows in your brain. While this may sound exotic and “biological”, in essence you are doing it all the time whenever you change your focus, get distracted, alter your strategy when solving a problem, etc. In the case of changing habits like binge eating, you will have to practice doing things in ways that are uncomfortable and “go against the grain” with respect to how you feel. You will need to become more aware of food cues effect you, and learn how to ignore them. You will need to practice behaviors that involve denying yourself rewards and making active choices throughout your day. You won’t be able to just “trust” how you are feeling, but will need to become more aware of what might actually be behind those feelings so that you can make more appropriate choices about how you are going to cope. You probably have a host of automatic thoughts that require a closer look, because you may have become really good at talking yourself into eating without realizing it, and have lost touch with ways to do the opposite. You already know that this is easier said than done. However, while all of these things are pretty challenging to accomplish, if you know what you are doing and why, your odds of getting results will improve tremendously.
For more on this, check out my post for Binge Eaters in the Tips and Tricks section.
Kessler, R.M., Hutson, P.H., Herman, B.K., Potenza, M.N. (2016). The neurobiological basis of binge-eating disorder. Neurosci Biobeh Rev. 63, 223-38.
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