Neurobiology of ED’s: Wiring and Tiring

If you are my friend and you have been around me for the past week, or so, you would probably already be sick of me quoting the book I’m currently reading to you. The book in question is a new release by Robert Sapolsky, a neurobiologist, entitled Behave: The Biology of Humans at Our Best and Worst. It’s a fascinating read for anyone who likes to explore the biological and physical underpinnings of things like aggression, fear, and anxiety.

So, it’s no surprise that I ended up thinking about the biological basis of disordered eating. Looking for information on it isn’t easy. What’s worse is that whatever studies you do find are written in a language that is frankly too convoluted for even a graduate student of psychology to decipher at first glance. Good thing I have a free evening.

Are there biological causes for anorexia?

Probably. Most of the theories at this point are just that – theories. I found a pretty comprehensive paper on the leading hypotheses and basically, what we know for sure at this time is that we don’t know much.

We know that anorexics have certain temperamental traits that leave them vulnerable to the disorder. Most of these appear already in childhood, and they are also traits that persist even after the anorexia goes into remission. If you’ve been reading my blog, you might have already seen the pattern: anxiety, perfectionism, lack of flexibility, obsessive behaviors, negative emotionality. Whether these things are more genetic or environmental is unknown (we know that it’s definitely both) – for now, there is no “anorexia gene,” as there are multiple things at play in the development of the disease.

kaye-2009-figure-1-adapted

As Sapolsky puts it, certain genes may be the cause of a certain disorder, but only within the context of a certain environment. For example, a person with an “anorexic” temperament may never develop the disorder unless they are subjected to Western body image ideals, strict parenting, rigid rules when growing up, etc. Obviously, it’s more complex than that, but you get the picture.

“Anorexic” traits.

Anxiety.

According to studies, anxiety is frequently comorbid with anorexia. What that means is that it occurs together with anorexia – it’s correlation, not causation, at this point; but it’s widespread – about 50% of the time, anorexics also score high on anxiety tests, in fact. Childhood anxiety is a better predictor of severe symptoms, and high anxiety is indicative of poor treatment outcomes.

Self-control.

As I have mentioned thousands of times, anorexia is about control a lot of the time. People with AN are ascetic, and able to delay or eliminate gratification for things that are necessary or wanted, as well as little reward reactivity. Basically, if a non-AN person gets a cookie, and they experience a 10 in terms of pleasure, for example, an AN person would probably be somewhere below 5.

Perfectionism.

We love self-imposed rules and standards. There’s a reason why getting anything less than an A in class is the end of the world for me. That’s bad news for the recovery process – perfectionism puts a lot of pressure on an anorexic to control their eating, even more, to find more creative ways of avoiding food, etc.

Harm avoidance.

Harm avoidance is a very complex trait, and it can include a bunch of things: anxiety, inflexibility, and inhibition, among others. It’s high in both ill and recovering anorexics. Fun fact: people with high HA are also less tolerant of uncertain situations. Huh, maybe that’s why I drive my friends up the wall with planning ahead for everything.

So what’s the biology?

Okay, this part is really hard to simplify, but I’m going to try to break it down for you guys.

Basically, the theory is that there are disturbances in the serotonergic and dopaminergic systems of the brain. Before you close the tab because I’m too technical here, hear me out. You’ve probably heard of serotonin and dopamine before. Those two are neurotransmitters, the chemical signals our neurons send to each other to communicate.

serotonin-pathways

Serotonin.

Serotonin is a substance that is associated with happiness, among other things. Serotonin is what makes our highs high, and a lack of it makes our lows low. Depressed people have low serotonin. Exercise increases serotonin production. Most new antidepressants are SSRI’s – selective serotonin reuptake inhibitors. What that means is that when we’re happy, to put it simply, one neuron produces serotonin and spits it out into the space between it and another

ssri-picture

neuron. The other neuron sucks it up and carries on the signal. What happens to the serotonin that’s left in the space? It gets sucked back up into the first neuron. What SSRIs do is block that sucking up and the serotonin is just left to chill between the cells, ready for the taking again. More serotonin – more happiness. Pretty simple.

Aside from happiness, serotonin also regulates a bunch of things, including (ding ding ding) satiety, impulse control, and mood.  Serotonin also helps animals adapt to aversive events – in this case, a lack of nutrition. Serotonin-related disturbances in the prefrontal cortex were found to be correlated with anorexia.

Dopamine.

Dopamine is another neurotransmitter. That’s the good stuff. Dopamine, for the most part, regulates reward. It’s what makes us feel good when we drink, smoke, snort cocaine, go bungee-jumping and beat up a bully. Dopamine is also what makes people with Parkinson’s disease tremble, as it is also an active component in our motor circuitry.

What happens with dopamine in anorexics, in simple English, is that not only is it depleted (also a sign of depression, a highly comorbid disorder in anorexia), but it also functions differently.

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Dopamine release in the precommissural dorsal caudate (I have a very vague idea of where in the brain that is, and honestly? Not that important) is associated with increased anxiety in recovered subject. Usually, dopamine would make you feel good and high, but in anorexics, it makes us anxious. What happens when people eat is that dopamine gets released, and generally, a person would feel satisfied and happy (“damn, that pizza was good”). With the dopamine having anxiety-generating effects in anorexics, food causes us to feel more anxious (“damn, I shouldn’t have eaten that pizza, oh my God, calories, oh my god, kilograms”). Pretty simple: food –> dopamine –> anxiety, so no food –> no dopamine –> no anxiety. Restricting one’s intake may then be just a way to reduce anxiety associated with eating – starvation becomes rewarding.

Appetite and food taste.

gustatory-pathway-cortex-in-insula-facial-and-glossopharyngeal-nerve-in-medulla-oblongataIt is theorized that the network which makes us enjoy the taste of certain foods is also implicated in the matter. The gustatory (taste-related) cortex of the brain is the anterior insula, and it works in conjunction with the anterior cingulate cortex and the orbital frontal cortex, to make our experience of food hedonistic.

There haven’t been many studies on the subject, but it looks like the insula is also kind of weird in anorexics – it doesn’t show as much activation as in controls on functional MRI scans. What that means is that the sense of taste, and, consequently, the associated pleasure, is then reduced. Even when hungry, there was less response than in healthy, non-AN controls. What that means is that anorexics not only experience less pleasure associated with food but also taste food less in general!

Reward and Control.

Other fMRI studies have shown that people with AN may have an imbalance in information processing in which they are less capable of identifying emotional significance of a particular stimulus (you can thank the ventral limbic neural circuit for that). To add to the damage, studies also show that the impaired dorsal executive function neural circuit, which controls planning and consequences, adds fuel to the flame. We have an inability to think about a stimulus as hedonistically rewarding. Instead, the reward we seek is more strategic in nature. That’s why anorexics just love rules and planning.

science_news_anorexic_brain_750_860

What I’m saying is, anorexia is so deeply-rooted that it actually alters your brain structure! Tell that to people who say “it’s all in your head!”

M-kay… that sounds pretty terrible. Is it curable?

Well, it’s treatable. What that means is that with extensive CBT and possible pharmacological therapy (such as antidepressants), an anorexic can potentially regain some semblance of normalcy. Temperamental traits are hard to change because they are so deeply embedded in our personalities;  but with enough repetitive activation of the damaged circuitry, the brain can relearn to be healthier. Probably not completely healthy, as anorexia is, unfortunately, a disorder that cannot be cured completely; but it can go into lengthy remission and cause less psychological and physical distress if managed with therapy and a proper, nutritious diet.

What we need now is to a) raise awareness and b) make neuroscientists get their asses in gear and ensure that these theories are right, and, if so, find ways of correcting all that screwed-up circuitry.

Source.

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