Biological Explanations of OCD (AQA A-Level Psychology): Revision Notes
Biological Explanations of OCD
Introduction to the biological approach
The biological approach emphasises the importance of physical processes in the body, particularly genetic inheritance and neural function, in explaining mental disorders like OCD. This perspective examines how an individual's genetic makeup may create vulnerability to OCD and how brain functioning in OCD sufferers differs from those without the condition.
Genetic explanations
Evidence for genetic vulnerability
Research suggests that genes play a significant role in determining individual vulnerability to OCD. Lewis (1936) conducted an early study examining family patterns of OCD and found that 37% of his OCD patients had parents with OCD, whilst 21% had siblings with the condition. These findings indicate that OCD tends to run in families, suggesting that genetic vulnerability rather than the certainty of developing OCD is inherited.
The diathesis-stress model explains this pattern - certain genes make individuals more susceptible to mental disorders, but environmental stress is typically required to trigger the actual development of the condition.
Candidate genes
Researchers have identified specific genes that create vulnerability to OCD, known as candidate genes. Some of these genes regulate the development of the serotonin system. For example, the 5HT1-D beta gene affects how efficiently serotonin is transported across synapses, which could impact mood regulation and contribute to OCD symptoms.
Polygenic nature of OCD
OCD appears to be polygenic, meaning multiple genes contribute to its development rather than a single gene causing the condition. Taylor (2013) analysed previous research findings and discovered evidence that up to 230 different genes may be involved in OCD. Many of these genes are associated with the functioning of dopamine and serotonin, both neurotransmitters that help regulate mood.
Different types of OCD
The genetic basis of OCD shows considerable variation between individuals. Different groups of genes may cause OCD in different people, a phenomenon described as aetiologically heterogeneous - meaning the origins of OCD have different causes. Evidence suggests that particular genetic variations may be linked to specific OCD subtypes, such as hoarding disorder and religious obsessions.
Evaluation of genetic explanations
Strengths:
Research Evidence: Twin Studies
Nestadt et al. (2010) reviewed previous twin studies and found compelling evidence for genetic influence:
- 68% of identical twins shared OCD
- Only 31% of non-identical twins shared the condition
This significant difference strongly suggests genetic influence on OCD development.
Limitations:
Too many candidate genes: Although twin studies suggest genetic control, researchers struggle to identify all the specific genes involved. Multiple genes appear to contribute, with each genetic variation only slightly increasing OCD risk. This makes genetic explanations less useful for prediction or treatment planning.
- Environmental risk factors: Environmental factors can also trigger or increase OCD risk, supporting the diathesis-stress model. Cromer et al. (2007) found that over half the OCD patients in their sample had experienced traumatic events, with more severe OCD occurring in those with multiple traumas. This suggests OCD cannot be entirely genetic in origin and may be more productive to focus on environmental causes since these are more modifiable.
Twin study limitations: Twin studies assume identical twins are only more similar genetically than non-identical twins, but overlook that identical twins may share more similar environments. Parents often treat identical twins more similarly (dressing them alike, buying same toys, sharing rooms), which could account for higher concordance rates rather than pure genetic factors.
Neural explanations
The role of serotonin
Neural explanations focus on how genes associated with OCD affect neurotransmitter levels and brain structures. Serotonin is a key neurotransmitter believed to regulate mood by relaying information between neurons. When serotonin levels are low, normal transmission of mood-relevant information cannot occur, affecting mood and sometimes other mental processes. Reduced functioning of the serotonin system in the brain may explain at least some cases of OCD.
Evidence supporting serotonin's role comes from antidepressant medications that work specifically on the serotonin system. These drugs increase serotonin levels and effectively reduce OCD symptoms, suggesting serotonin dysfunction contributes to the disorder.
Decision-making systems and brain structures
Some OCD cases, particularly hoarding disorder, appear linked to impaired decision-making abilities. This may result from abnormal functioning of the lateral frontal lobes - brain areas behind the forehead responsible for logical thinking and decision-making.
Research also indicates that the left parahippocampal gyrus, a brain region associated with processing unpleasant emotions, functions abnormally in OCD patients.
Evaluation of neural explanations
Strengths:
- Supporting evidence: The effectiveness of serotonin-specific antidepressants in reducing OCD symptoms supports the role of serotonin dysfunction. Additionally, OCD symptoms occur in other biologically-based conditions like Parkinson's Disease (Nestadt et al. 2010), suggesting shared biological processes may be responsible.
Evidence for direct serotonin involvement: Antidepressants that don't work on the serotonin system have no effect on OCD, indicating serotonin is directly involved in OCD rather than just accompanying depression (which commonly co-occurs with OCD).
Limitations:
- Unclear neural mechanisms: Studies show that neural systems functioning abnormally in OCD are the same systems involved in normal decision-making (Cavedini et al. 2002). However, research has identified various brain systems that may be involved sometimes, but no system consistently plays a role in all OCD cases. Therefore, we cannot claim to fully understand the neural mechanisms involved.
Causation vs correlation: Evidence shows various neurotransmitters and brain structures don't function normally in OCD patients, but this doesn't prove abnormal functioning causes OCD. These biological abnormalities could be results of OCD rather than its causes.
- Co-morbidity with depression: Many OCD sufferers also become depressed, a phenomenon called co-morbidity. Depression likely involves serotonin system disruption, creating a logical problem when attributing OCD to serotonin dysfunction - it could be that serotonin disruption occurs because patients are also depressed.
Key Points to Remember:
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Genetic vulnerability: Strong evidence from twin studies (68% concordance in identical twins) suggests genetic influence, but OCD is polygenic involving up to 230 different genes
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Environmental factors matter: The diathesis-stress model shows genes create vulnerability, but environmental triggers are often necessary for OCD development
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Serotonin dysfunction: Low serotonin levels may disrupt mood regulation, supported by the effectiveness of serotonin-specific antidepressants in treating OCD
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Brain structure involvement: Abnormal functioning in lateral frontal lobes (decision-making) and parahippocampal gyrus (processing unpleasant emotions) may contribute to OCD symptoms
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Limitations exist: Both genetic and neural explanations face challenges - genetic approaches struggle with too many candidate genes, whilst neural explanations cannot establish clear causation and may confuse correlation with co-morbid depression