Explaining OCD Flashcards
(20 cards)
What is a concordance rate?
The likelihood that two people will share the same characteristic
What is a candidate gene?
Gene that causes a disorder
What are the two candidate genes involved in OCD? (genetic explanations for OCD)
- SERT-gene
- COMT-gene
How does the COMT gene contribute to OCD?
- regulates the production of dopamine
- One allele of high levels of dopamine and is common in people with OCD
- Tukel et al
- overactive reward system may explain compulsion + rewards felt
How does the SERT gene contribute to OCD?
- Serotonin transporter gene
- Mutation of the gene causes low levels of serotonin found in families with OCD (Ozaki et al)
What does Taylor say about the genes of OCD?
- OCD is polygenic
- found 230 genes that may be involved in OCD
Where does evidence for heritability of OCD come from?
- family and twin studies
- concordance rate between someone and random stranger is 2%
- However with OCD, more genetically close = higher concordance rate
- MZ Twins = 68%
- DZ Twins = 31% (share 50% of DNA)
What does the neural explanation of OCD relate to?
- Brain structures
- Neurotransmitters
What are the two neurotransmitters linked to OCD?
- Serotonin: stabilises and regulates mood, low levels linked to OCD
- Dopamine: linked with reward-motivated behavior, overactive system
What are the neural structures linked to OCD?
Worry circuit:
- Orbital frontal cortex
- Basal ganglia system , caudate nucleus
- thalamus
What happens in the worry circuit for people with OCD?
communications with the structures in the worry circuit are overactive
- overactive orbital frontal cortex
- abnormal function of caudate nucleus
What is the role of the basal ganglia?
- involved in coordination and movement
- stops unwanted movement
- if working abnormally like in OCD it leads to unwanted involuntary movement
- Patients who suffer from brain injuries in this region often develop OCD like symptoms - following recovery
What is the role of the OFC?
- Converts sensory information into thoughts + actions
- If it picks up danger sends worry signals to the thalamus
What is the role of the thalamus?
- relays information to other parts of the brain to take action
- signal sent back to the OFC to confirm the worry
What is the role of the caudate nuclues?
- Between the OFC and Thalamus
- Intercepts signal
- Usually suppresses worry signal
- so not every worry signal is sent to thalamus
How does serotonin influence the worry circuit?
- serotonin works as an inhibitor
- normal person, serotonin inhibits the worry signals
- OCD patients have low levels of serotonin, so impulses are not inhibited
A03 - Genetic explanation has supporting evidence
- Supporting evidence comes from Nestadt who looked at family studies of first degree relatives
- people with a first degree relative with OCD had a 5-times greater risk of having the illness at some point in their lives
- meta analysis of 14 twin studies of OCD found that on average MZ twins were more than twice as likely to develop OCD if their co-twin had the disorder than was the case for DZ twins
- Suggests the greater amount of genes shared the more likely the person will develop OCD, thus supporting the genetic explanation
A03 - Genetic explanation may only explain a vulnerability to OCD
- Cromer et al found that over half the OCD patients in their sample had a traumatic event in their past
- Those who had more severe OCD had more than one trauma
- OCD cannot be entirely genetic in origin and that environmental factors may play a fundamental cause in OCD
- Suggests that the diathesis model is more appropriate explanation for OCD
A03 - Evidence to support the neural explanation
- The neural explanation suggests that low levels of serotonin and high levels of dopamine result in OCD
- Evidence has shown that antidepressants that increase the production of serotonin are effective in reducing the symptoms of OCD (Soomro et al)
- If increasing serotonin reduces the symptoms, then low levels of serotonin must have some role to play in the symptoms of OCD
- Therefore supports the neural explanation
A03 - More than one brain structure
- Other areas of the brain such as the parahippocampul gyrus and the prefrontal cortex and other areas of the brain are also linked with OCD
- like genes, there are vast number of brain structures involved in OCD that are functioning abnormally in some people
- However no system can be found that always plays a role in OCD
- This means that it is difficult to establish a single neural mechanism involved. Therefore neural explanation gives us little insight into the cause of OCD meaning it is a limited explanation of OCD.
