THE BIOLOGICAL APPROACH TO EXPLAINING OCD

~GENETIC EXPLANATIONS~

STUDY:

Psychologist observed that, of his OCD patients, 37% had parents with OCD, and 21% had siblings with OCD

CONCLUSION:

This suggests that OCD runs in families

~DIATHESIS-STRESS MODEL~

According to the diathesis-stress model, certain genes leave some people more likely to develop a mental disorder, but it is not certain - some environmental stress (experience) is necessary to trigger the condition

~CANDIDATE GENES~

→ Some genes are involved in regulating the development in serotonin system

→ E.g. the gene 5HTI-D beta is implicated in the transport of serotonin across synapses

~OCD IS POLYGENIC~

→ This means that OCD is not caused by ONE single gene, but instead by a combination of genetic variations that together significantly increase vulnerability

STUDY:

• Psychologist analysed findings of previous studies and found evidence that up to 230 different genes may be involved in OCD

• One group of genes may cause OCD in one person but a different group of genes may cause the disorder in another person

EVALUATION

Research Support

→ RESEARCH SUPPORT

• One strength of the genetic explanation for OCD is the strong evidence base.

• There is evidence from a variety of sources which strongly suggests that some people are vulnerable to OCD as a result of their genetic make-up. One source of evidence is twin studies. It has been found that 68% of monozygotic twins shared OCD as opposed to 31% of dizygotic twins.

• Another source of evidence is family studies. It has been found that a person with a family member diagnosed with OCD is around 4 times as likely to develop it compared to someone without.

• These research studies suggest that there must be some genetic influence on the development of OCD.

Conflicting Evidence

→ ENVIRONMENTAL RISK FACTORS

• One limitation of the genetic model of OCD is that there are also environmental risk factors.

• OCD does not appear to be entirely genetic in origin as it seems that environmental risk factors can also trigger or increase the risk of developing OCD.

• In one study, it found that over half the OCD clients in their sample had experienced a traumatic event in their past. OCD was also more severe in those with one or more traumas.

• This means that genetic vulnerability only provides a partial explanation for OCD.

~NEURAL EXPLANATIONS~

→ The genes associated with OCD are likely to affect the levels of key neurotransmitters, as well as structures in the brain

~THE ROLE OF SEROTONIN~

→ Neurotransmitters are responsible for relaying info from one neuron to another

→ Low levels of serotonin inhibit normal transmission of mood-relevant info, and so they experience low moods

~DECISION-MAKING SYSTEMS~

→ Impaired decision-making may be associated with abnormal functioning of the lateral sides of the frontal lobes

→ There is also evidence to suggest that the left parahippocampal gurus, associated with processing unpleasant emotions, functions abnormally in OCD

EVALUATION

Research Support

→ RESEARCH SUPPORT

• One strength of the neural model of OCD is the existence of some supporting evidence.

• Antidepressants that work purely on serotonin are effective in reducing OCD symptoms, suggesting that serotonin may be involved in OCD.

• Also, OCD symptoms form parts of conditions that are known to be biological in origin (e.g. Parkinson’s).

• This suggests that biological factors may also be responsible for OCD.

Conflicting Evidence

→ NO UNIQUE NEURAL SYSTEM

• One limitation of the neural model is that the serotonin-OCD link may not be unique to OCD.

• Many people with OCD also experience clinical depression (co-morbidity).

• This depression probably involves disruption to the action of serotonin, leaving us with the question of if serotonin activity levels are just disrupted due to the person being depressed.

• This means that serotonin may not be relevant to OCD symptoms.