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Anorexia: Biological explanations

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  • Anorexia: Biological explanations

Biological etiologies of anorexia

The biological approach argues that both genetics and neurochemistry may explain the origin of eating disorders.  For this component of the module, you will learn about both the genetic argument and the role of neurotransmitters in the brain. The biological approach is often considered a reductionist approach to understanding mental health - and it is the basis for medical treatment.

Key concepts

Before completing the module below, please read the section of the textbook called Biological approach to anorexia nervosa. When reading this section, please make note of the following important concepts:

  • Candidate genes
  • Diathesis-stress model
  • Neurotransmission
  • Reductionism vs holism
  • Twin studies

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Deepening our understanding

Watch the following video and then answer the questions below. Try to answer the questions by writing a response in your notebook before looking at the "correct" answer that is provided.  This will help you to remember the material after you have left this part of the module.

Questions

1.  The first study described is by Foerde et al (2015). What does this study tell us about the potential role of the dorsal striatum in anorexia?

The study indicates that participants with anorexia showed much more activity in the dorsal striatum when making food choices than did the control participants. This part of the brain is linked to habit formation.  It could mean that dysfunctional eating behaviours are not so much a choice, but a habit that needs to be broken.

2. The second study described is by Bailer & Kaye (2011).  What does this study tell us about the potential role of the insula in anorexia?

The insula allows us to experience pleasure through taste. It appears that the insula may not function in this manner for anorexics. This would mean that the subsequent increase in dopamine which an individual would experience from the positive experience would not follow, leading to a lack of motivation to eat or continue eating.

3. What concerns would you have about the two studies in this video? What are their key limitations?

Both of the studies are quasi-experimental.  This means that a cause and effect relationship can not be established.  In addition, the studies are cross-sectional - that is, they are not longitudinal studies, measuring eating and brain activity over time.  Finally, the studies are not prospective. The brain activity of the participants with anorexia was not measured prior to the onset of the disorder, so it cannot be known to what extent the brain activity is a cause or an effect of the disorder.

Biological explanations: Theories and research

Read through the following presentation.  In the presentation, you will see two sets of slides to "check for understanding."  One set of statements about genetics and one about neurochemistry.  For each set of statements, decide whether the statements are true or false.  You should be able to justify your position.  It is best if you write about your response before checking your work below.

Checking for understanding: Genetics

1.  False.  Twin studies alone are not able to tell researchers which genes are actually involved in the behaviour.  They only indicate that the likelihood that the disorder is inherited.

2.  True.  Genome-wide Association Studies (GWAS) use very large samples and have been able to identify candidate genes for anorexia. For example, the study by Scott-van Zeeland (2014) identified the potential role of the EPHX2 gene.

3.  True.  Although you could still consider the role of an individual gene reductionist, modern biologists recognize a gene x environment interaction - not limiting the behaviour simply to the existence of the gene.  It is, to be fair, still pretty reductionist to argue that the behaviour is the result of gene expression.

4.  False.  This is true in human research, but researchers have been able to manipulate genes in animal research.

5.  False. If the twin study is an adoption study, then there is an attempt to do this, but it is impossible to completely discount the role of the environment.

6.  True. This means that there must be other factors involved in the symptoms of anorexia (e.g. feelings of guilt vs shame).

7.  True.  Although we know that the EPHX2 gene plays a role in cholesterol, we are not sure exactly how that is linked to the onset of eating disorders.

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Checking for understanding: Neurochemistry and the brain

1.  False. Starvation appears to be used as a means of lowering one's level of serotonin.  The theory is that starvation lowers levels of serotonin, but the brain increases the number of receptor sites.  Eating, then, leads to feelings of anxiety.  In order to decrease these feelings of anxiety, the individual engages in more calorie restriction.

2.  False. The study was quasi-experimental. The patients with anorexia and healthy participants could not be randomly allocated to conditions. 

3.  True. The sample size was only 21 women.  The sample does not include males with anorexia and the participants in the study were all receiving treatment at a clinic.

4.  False.  The study is cross-sectional.  In addition, the women were not showing symptoms of anorexia at the time of the study.

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The use of animal models: The ABA rat

One of the ways that experimental research can be carried out to investigate the etiology of anorexia is through animal research. To do this, researchers use the ABA rats. Activity-based anorexia [ABA] is a phenomenon that can be induced in rats that models the key symptoms of anorexia nervosa. When rodents with free access to voluntary exercise on a running wheel experience food restriction, they become hyperactive – running more than animals with free access to food.

Chiye Aoki is one of the leading researchers using ABA rats to study anorexia.  What would be your concern about using such an animal model?

Evaluating theories

The following section looks at how we can evaluate these two theories.  Think about the questions below - and then use the flashcards below to see how well you were able to evaluate the theories.

TEACUP and neurobiological theories

One of the ways to evaluate a theory is to use TEACUP:

  • Is the theory empirically testable?
  • Is there evidence to support the theory?  What is the quality of that evidence?
  • Are there applications of the theory?  How good are those applications?
  • What are the constructs that are relevant to the theory?  How well can psychologists measure these constructs?
  • Is the theory unbiased? 
  • Does the theory predict behaviour?  Or is the theory only explanatory?

Checking for understanding

By now, you should have a good understanding of the strengths and limitations of the theory that anorexia nervosa is caused by neurobiological factors. Could you do the same thing now for the theory of genetic vulnerability?

In the box below, write the "evaluation paragraph" in an essay where you have been asked to "Evaluate one biological explanation of one disorder."  Assume that you have already written the rest of the essay - that is, you have already explained the theory and described relevant research. Explain two or three evaluation points with regard to the theory - do not try to do all aspects of TEACUP!

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Continue to cognitive explanations of anorexia nervosa