What is the difference between MZ and DZ twins in the context of Anorexia Nervosa research?

MZ (monozygotic) twins share 100% of their genes, while DZ (dizygotic) twins share about 50%. Higher concordance rates in MZ twins suggest that the disorder has a significant genetic basis rather than being purely environmental.

How does the role of Serotonin differ from Dopamine in biological explanations of AN?

Serotonin is primarily linked to anxiety, perfectionism, and appetite suppression, often showing overactivity. Dopamine is linked to the reward system, where AN patients may show a blunted response to the pleasure of food but a heightened response to the 'reward' of starvation.

What is the distinction between a 'state' and a 'trait' in biological research?

A 'trait' is an innate biological characteristic that exists before the illness begins, while a 'state' is a biological change that occurs as a result of the illness (e.g., due to starvation). Distinguishing between them is crucial for identifying true causes.

Why is it a mistake to assume a single gene causes Anorexia Nervosa?

AN is a polygenic disorder, meaning it results from the interaction of many different genes, each having a small effect. Attributing it to one gene ignores the complex biological and psychological nature of the condition.

What is the 'starvation effect' error in interpreting brain scan data?

The error occurs when researchers assume brain abnormalities seen in active AN patients are the cause of the disorder. In reality, many of these changes are the physical consequence of severe malnutrition and may disappear after recovery.

Why is biological determinism a pitfall in understanding eating disorders?

Biological determinism suggests that genes dictate behavior entirely. This is incorrect because environmental factors, such as culture and family dynamics, play a critical role in whether a genetic predisposition actually manifests as a clinical disorder.

Define 'Concordance Rate' in the context of genetic studies.

The concordance rate is the probability that if one individual has a disorder, their relative (e.g., a twin) will also have the disorder. It is used to measure the relative contribution of genetics versus environment.

What is the 'Insula' and why is it relevant to AN?

The insula is a brain region involved in interoceptive awareness, or the perception of internal bodily sensations. In AN, dysfunctional insula activity is linked to distorted body image and a lack of recognition of hunger signals.

What does 'Polygenic' mean in relation to mental health disorders?

Polygenic means that a trait or disorder is influenced by multiple genes acting together. This explains why there is no single 'cure' or simple genetic test for complex conditions like Anorexia Nervosa.

How does the Hypothalamus contribute to the symptoms of Anorexia?

The hypothalamus regulates the body's 'set point' for weight and hunger. If its functioning is impaired, the normal biological drives to seek food and maintain a healthy weight are disrupted, facilitating self-starvation.

Biological Explanations for Anorexia Nervosa | AQA A-Level Psychology

Eating behaviour: Option Topic (Section C)

Biological Explanations for Anorexia Nervosa

Summary

Biological explanations for Anorexia Nervosa (AN) focus on the internal physical mechanisms that predispose individuals to the disorder and maintain its symptoms. This perspective encompasses genetic vulnerability, neurochemical imbalances in neurotransmitter systems, and structural or functional differences in specific brain regions responsible for appetite, reward, and body perception.

1. Genetic Vulnerability and Heritability

Heritability Estimates: Research into the genetics of Anorexia Nervosa suggests a significant hereditary component, with heritability estimates typically ranging from $40\%$ to $60\%$ . This indicates that a substantial portion of the variance in the risk for developing AN can be attributed to genetic factors rather than purely environmental influences.
Twin Study Methodology: Scientists compare concordance rates between monozygotic (MZ) twins, who share $100\%$ of their DNA, and dizygotic (DZ) twins, who share approximately $50\%$ . A significantly higher concordance rate in MZ twins compared to DZ twins provides strong evidence for a genetic basis for the disorder.
Polygenic Nature: AN is considered a polygenic condition, meaning it is not caused by a single 'anorexia gene' but rather by the cumulative effect of hundreds or thousands of genetic variants. These variants may influence personality traits such as perfectionism, anxiety, and obsessive-compulsiveness, which are known risk factors for eating disorders.

Diagram of the human brain highlighting the hypothalamus (appetite regulation) and the insula (body perception), which are key areas involved in biological explanations of Anorexia Nervosa.

2. Neurotransmitter Dysregulation

The Serotonin Hypothesis: Serotonin (5-HT) is a neurotransmitter involved in mood regulation and appetite suppression. In individuals with AN, there is evidence of altered serotonin activity, specifically overactivity in certain pathways that may lead to high levels of anxiety and perfectionism, which the individual attempts to manage through restrictive eating.
Dopamine and Reward Processing: Dopamine is central to the brain's reward system, signaling the pleasure derived from activities like eating. Research suggests that individuals with AN may have a dysfunctional dopamine system, leading to a decreased reward response to food and an increased reward response to the 'achievement' of weight loss.
Interaction with Starvation: It is important to distinguish between innate neurochemical traits and the effects of starvation. Chronic malnutrition can alter neurotransmitter levels, creating a feedback loop where the biological changes caused by dieting further reinforce the disordered eating behavior.

3. Neural Circuitry and Brain Structure

4. Key Distinctions in Biological Research

5. Exam Strategy & Tips

6. Common Pitfalls & Misconceptions