If you need to catch up, you can find parts one and two here.
Like the 5-HT neuronal system, dopamine is implicated in the neurocircuit function of AN-R. The dopamine system has often been referred to as the reward and pleasure centre of the brain. It is the neurotransmitter that rewards us when we do something we enjoy, and also rewards us when we avoid something unpleasant. It plays a huge role in addiction and addictive behaviours, and initially my paper was going to be on the question of whether or not eating disorders can be classified as an addiction, but that proved to beyond the scope of this assignment and its restrictive word limit. I did, however, read some very interesting papers about the addictive nature of eating disorders such as binge eating disorder, bulimia, and anorexia nervosa binge-purge subtype. Perhaps I will write a post about it in future.
The following is verbatim from my original paper with my added commentary in purple.The dopamine neurotransmitter system regulates eating behaviour through the modulation of motivation for dietary intake and other reinforcement- and stimulus-reward associations (Frank, 2014; Volkow et al., 2003). In particular, the dopamine D1 and D2 neurotransmitter receptors are involved in motivated food approach and fear extinction, while the D2/D3 receptors bind in the ventral striatum, a region of the brain that regulates responses to reward stimuli (Kaye et al., 2009). Further, studies have suggested that restricted food intake and high levels of exercise engage the mesolimbic dopamine neurons—part of the brain’s reward system—thereby rewarding this behaviour in AN-R (Sodersten et al., 2016). The dopaminergic pathways, therefore, could be an important component of the neurobiology of AN-R. Hopefully this is clear enough as it is – it is basically saying, dopamine plays a role, and here’s how.
A number of studies have documented altered dopamine function in AN-R. For example, one study found that the major dopamine metabolite, cerebrospinal homovanillic acid, was reduced to about 30% in individuals with AN-R compared to healthy controls, suggesting decreased intrasynaptic dopamine levels (Kaye et al., 1984, cited in Frank, 2014). In a related study, positron emission tomography (PET) imaging revealed that, compared to healthy controls, individuals with AN-R had increased dopamine D2/D3 receptor binding in the anterior ventral striatum, suggesting a hypersensitivity to these pathways (Frank, 2014; Frank et al., 2005). This hypersensitivity may contribute to the altered reward processing seen in AN-R, whereby hunger is rewarded by a reduction in dysphoric mood (Kaye, 2008; Via et al., 2015). So basically, compared to healthy controls/people without AN-R, people with AN-R have a hypersensitivity to dopamine. This hypersensitivity means that the wrong thing is rewarded; instead of finding food pleasurable and rewarding, people with AN-R find hunger rewarding because it reduces their anxiety. Further, there are some studies that suggest that starvation can feel euphoric and similar to the high that drug users get when they take their drug of choice. I was going to link to some articles here, but now I feel like they may be taken as encouragement or "tips" so I've decided not to. Moreover, D1 and D2 receptors [D1 and D2 are types of dopamine] can be found in human skin, raising the possibility that abnormal function of these receptor systems could contribute to the disturbances in body perception present in AN-R (Tammaro et al., 2012, cited in Frank, 2014).
This point needs to be emphasised. Have you, if you are a person with an ED – and maybe even if you aren’t but you do have body image issues – ever eaten something and then felt like you were expanding right then and there? And I don’t mean, oh, haha, I’m getting fatter/I need to burn off that doughnut/I ate too much and I feel bloated. I mean actually, distressingly, feel like you are swelling and blowing up like a balloon and soon you’re going to pop your buttons and soar out the window like Harry’s obnoxious aunt?
|Gif from MuggleNet|
I'm being facetious, but rest assured it is anything but funny when it is happening. It is a highly distressing, upsetting, and difficult experience. It is grabbing at your skin and groping your stomach and clutching the bones of your back, your hips, your ribs, because you’re sure there’s more flesh there than there was this morning, you’re just sure of it. It is trying on every pair of jeans you own at 3am because even though you wore jeans yesterday, they could not possibly fit anymore because you ate two apples today instead of one*. It is crying, hysterically so, at 12 years old at the dinner table because your mom said you have to eat your dinner but you can’t, you can’t, you can’t, your skirt is getting tighter by the second and your body is swelling like you’ve been stung by a million bees and why are they all just staring at you and not helping you when clearly you’re about to explode and flood the room with all the putrid bile-coloured fat coursing through your veins?? It is horrible and it is hard and it scary, and it is [theoretically, as this is a theory] because of the faulty dopamine circuitry in your brain. It is [theoretically] the D1 and D2 receptors in your skin going haywire and giving your brain misinformation. That misinformation can then be translated back to your eyes where you then look at yourself and see yourself as bigger than you are. Perhaps you have heard about – or experienced – the phenomena of being told you are underweight or that you’ve lost weight or that you look thinner or whatever people may say [PSA pls don’t comment on other people’s bodies unless they ask okay thx friends], or perhaps you’ve stepped on the scale and seen a number that is dramatically lower than it used to be, yet you look exactly the same. Or worse, to the sick mind, bigger**. That, my friends, is the dopamine. Perception is tricky as heck and what you see and what your brain interprets as what you see can be two very different things even without the dopamine deciding to further screw things up. Dopamine is one sneaky little bastard and can wreak havoc on the disordered brain.
Anyway. Moving right along.
Similarly, there is increasing literature suggesting that fear extinction consolidation relies on prefrontal cortical dopamine D1 and D2 receptor stimulation (Mueller, Bravo-Rivera, & Quirk, 2010, cited in Frank, 2014). Fear extinction consolidation means exactly what it sounds like it means – the consolidation of the fear extinction. You can overcome a fear and do the scary thing once, twice, ten times, but a fear is not extinct until that extinction has been consolidated and you are no longer afraid of that stimulus. In this case, the stimulus is food and weight gain, as I am about to discuss…Now. One of the core symptoms of AN-R is an intense fear of weight gain or becoming fat, and so altered stimulation of D1 and D2 receptors provides one possible explanation for this heightened fear response and the difficulty in overcoming it and associated fears regarding food intake. To be clearer, the dysregulation of D1 and D2 means that a person with AN-R has an impaired ability to extinguish/overcome fears, and given that a core fear for those with AN-R is food and the associated weight gain, this fear is even harder to tackle and overcome because a) the mere act of eating causes a whole host brain shenanigans, as discussed in parts one and two, and b) eating further messes with said D1 and D2 receptors, which messes with the ability to overcome fears while simultaneously sending faulty signals about the body to brain and telling the brain that the body is already too big or getting bigger or expanding and swelling and suffocating and choking and I can’t breathe under the weight of my own body I am crushing myself from the outside in…So yay. We be screwed. Lol.
And that cheerful note concludes part three. Lol. I’m kidding, by the way. People with AN-R are not screwed, but it is a very difficult disorder to treat and overcome as I’m sure you’re all starting to see, if you don’t already know from personal experience. Hopefully post this has been clear and informative. If my information or interpretation is incorrect, please feel free to let me know and provide me with further studies or information so that I may learn more and correct any mistakes. As always, my disclaimer here is that I am only a psych student, not a qualified anything to do with mental health, and the extent of my formal research into this topic was only this paper. I do not claim to know everything there is to know, nor do I claim to understand it all. Please take my interpretations as interpretations, not facts. The full reference list is under the spoiler, so if you’d like to read more, I used 30 or 40 research articles to put this paper together and you are more than welcome to follow these things up at their original source.
Coming up in my next post: Hunger Hurts But Starving Works Part Four: Dopamine, food hoarding, food obsession, and giving rats anorexia [this is a real thing. Madness.]
Feel free to drop me a comment via the comments, twitter, Instagram, tumblr, and/or askFM if you have questions or want to talk about any of the things I've discussed.
*This is an over-exaggeration to make my point. Few people live solely on an apple a day. Some do. But most eat more, quite a bit more according to my research, but I am not going to talk about the actual numbers because it is not about that.
**Worse to the disordered brain, not worse in general. There's nothing wrong with gaining weight and I don't mean to imply there is. I'm just talking about gaining weight from the perspective of a person with a disorder that makes weight gain seem like the scariest thing on the planet.
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