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Biological Explanation of Obsessive-Compulsive Disorder (OCD)

Biological Approach Outline

1

Genetic Explanation

Evidence from family and twin studies, highlighting polygenic influence.
2

Neural Explanation

Focus on CSTC circuit dysfunction and roles of key neurotransmitters.
3

Biological Treatment

Analysis of drug therapy (SSRIs) and its effectiveness.

Key Biological Terms

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Polygenic

Meaning many genes contribute small effects rather than one single gene causing the disorder.
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CSTC Circuit

Cortico-striato-thalamo-cortical loop; dysfunction is implicated in OCD symptoms.
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Serotonin

Low levels are linked to OCD symptoms because it helps regulate mood and anxiety.
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SSRIs

Selective Serotonin Reuptake Inhibitors; drugs used to increase serotonin levels in the brain.

Genetic Evidence Overview

Genetic studies provide strong evidence for the heritability of OCD:

Study Type Finding Implication
Lewis (1936) 37% of patients had a parent with OCD. Suggests high heritability
Twin Studies Higher concordance in MZ vs DZ twins. Supports genetic influence
Candidate Genes Identify SERT gene, involved in serotonin regulation. Specific vulnerability

Neural Dysfunction Focus

Role of Key Brain Regions

Overactivity in the Orbitofrontal cortex may send excessive "danger" signals that something is wrong, leading to obsessive thoughts. If the Caudate nucleus is dysfunctional, it fails to suppress these minor worries, allowing unchecked worry signals to reach the thalamus, triggering compulsions.

Cortico-Striato-Thalamo-Cortical (CSTC) Circuit

OFC → Caudate Nucleus → Thalamus (Worry Loop)
Dysfunction in this brain loop leads to constant worry signals not being suppressed, resulting in ritualistic compulsive behaviours.

Drug Therapy Evaluation

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AdvantagesEffective for many patients (50-60%); useful when psychological therapy is not accessible; relatively fast-acting in reducing symptoms.
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DisadvantagesCommon side effects (nausea, sexual dysfunction); not universally effective; symptoms often return (relapse) if medication is stopped.

Mechanism of SSRI Action

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Correcting the Imbalance: Medications aim to correct chemical imbalances. By increasing serotonin, drugs may normalize functioning in the CSTC circuit and reduce the excessive anxiety driving compulsive behaviours.

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Biological Approach OCD Deck
Q
Biological Approach Emphasis

What does the biological approach to OCD emphasize?

A
Answer

Biological factors like genetics, brain structure and function, and neurochemistry as causes of OCD.

Q
Genetic Evidence

What evidence supports the genetic explanation of OCD?

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Answer

Family and twin studies showing higher OCD rates among relatives and higher concordance in identical twins.

Q
Polygenic Meaning

What does "polygenic" mean in relation to OCD?

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Answer

Many genes contribute small effects to vulnerability rather than one single gene causing OCD.

Q
Key Brain Circuit

Which brain circuit is most implicated in OCD?

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Answer

The cortico-striato-thalamo-cortical (CSTC) circuit.

Q
Orbitofrontal Cortex Role

What is the role of the orbitofrontal cortex in OCD?

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Answer

Overactivity sends excessive "danger" signals, causing obsessive thoughts.

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Caudate Nucleus Contribution

How does the caudate nucleus contribute to OCD symptoms?

A
Answer

Damage reduces its ability to suppress minor worries, leading to compulsions.

Q
Main Neurotransmitter

Which neurotransmitter is most associated with OCD?

A
Answer

Serotonin.

Q
SSRIs and OCD

What are SSRIs and how do they help OCD?

A
Answer

Selective Serotonin Reuptake Inhibitors; they increase serotonin levels, reducing OCD symptoms.

Q
Tricyclic Antidepressant

Name a tricyclic antidepressant used for OCD.

A
Answer

Clomipramine.

Q
Drug Therapy Disadvantages

What are some disadvantages of drug therapy for OCD?

A
Answer

Side effects, not effective for all, and symptoms may return if stopped.

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🧠 OCD Biology Quiz

1. Which brain circuit is primarily implicated in OCD?

The CSTC circuit involves brain regions linked to impulse control and emotion regulation that show dysfunction in OCD.

2. Which neurotransmitter is mainly targeted in the biological treatment of OCD?

SSRIs increase serotonin levels, which are low in many OCD patients, helping reduce symptoms.

3. What percentage of OCD patients, according to Lewis (1936), had a parent with the disorder?

Lewis found 37% of OCD patients had a parent with OCD, indicating a genetic component.

4. Which is NOT a known disadvantage of drug therapy for OCD?

Drug therapy manages symptoms but is not a cure; therapy is often still needed.

5. Twin studies show higher concordance for OCD in:

Monozygotic (identical) twins share more genetic material, showing higher OCD concordance.

📊 Results

  • Notes and Quiz
  • Psychology
  • AS & A Level
  • Mental Health Therapies
  • AQA