The Biological Approach to Explaining OCD

Question 1

Genetic explanations

Answer 1

• Condition characterized by compulsive behaviour
• Obsessions = cognitive
• Compulsions = behavioural
• Genes consist of DNA and codes for physical features of an organism
• Inherited from parents to offspring
• Lewis (1936): 37% of his patients had parents with OCD, 21% had siblings with OCD.
• Genetic factor to OCD, but it is vulnerability, not certainty.

Question 2

Diatheses-Stress Model

Answer 2

• Certain genes make some more likely to develop a mental disorder.
• Environmental stress (experience) triggers the condition.

Question 3

Candidate Genes

Answer 3

• Genetic regulation of serotonin system.
• Gene 5HT1-D beta implicated in transport of serotonin across neural synapses.
• Low serotonin = low mood, high serotonin = elevated mood.

Question 4

OCD is Polygenic

Answer 4

• Cause by combination of genetic variations – not a single gene!
• Taylor (2013): up to 230 genes involved with OCD. Example: action of neurotransmitters dopamine and serotonin.

Question 5

Neural Explanations

Answer 5

• Physical and psychological characteristics are determined by behaviour of nervous system: brain and individual neurons.

Question 6

Role of serotonin

Answer 6

• Neurotransmitters relay info from one neuron to next.
• Low serotonin = low moods.
• Some OCD explained by reduction in functioning of serotonin system in brain.

Question 7

Decision Making Systems

Answer 7

• Some OCD associated with impaired decision-making (e.g., hoarding).
• May be associated with abnormal functioning of lateral frontal lobes of brain.
• Parahippocampal gyrus associated with processing unpleasant emotions functions abnormally in OCD.

Question 8

Evaluation
research support

Answer 8

• Strength: strong evidence.
• Vulnerability due to genetics.
• Nestadt et al. (2010): reviewed (meta-analysis) twin studies: 68% monozygotic twins share OCD vs 31% dizygotic.
• Marini and Stebnicki (2012): OCD diagnosis 4 times more likely if family member has OCD.

Question 9

Environmental Risk Factor:
eval

Answer 9

Environmental Risk Factor:
- Limitation: genetic variation makes one more vulnerable to OCD, but OCD origin not entirely genetic.
- Cromer et al. (2007): 50% of OCD clients in sample experienced traumatic event in past. OCD more severe in those >1 trauma.

Question 10

Animal Studies: eval

Answer 10

• Ahmari 2016: animal studies show some genes associated with repetitive behaviours, such as mice.
• Brain of human vs mouse vary in complexity, so may not be able to generalize to human OCD.

Question 11

eval
Research Support:
anti

Answer 11

• Strength: Antidepressants (focused on serotonin) effective in reducing OCD symptoms. Supports link of serotonin to OCD.
• Nestadt et al. (2010): OCD symptoms part of known biological conditions like Parkinson’s disease.
• If biological disorder produces OCD symptoms, assume biological processes underlie OCD.

Question 12

No Unique Neural System: eval

Answer 12

• Limitation: serotonin-OCD link may not be unique to OCD.
• OCD patients also have clinical depression (co-morbidity).
• Depression probably involves disruption to action of serotonin. Logical problem: could it simply be that serotonin activity is disrupted in many people with OCD because they are also depressed? Serotonin may not be relevant to OCD symptoms.

Question 13

Correlation and Causality:

Answer 13

• Neural systems (like serotonin) do not work normally for OCD patients.
• This explains brain dysfunction causing OCD.
• A correlation between neural abnormality and OCD… but is it causal? Is there a third factor?