The Biological Approach to explaining OCD Flashcards
What are the key assumptions of the Biological Approach?
All behaviour has a physical cause.
Abnormal behaviour e.g. OCD, is likely to be caused by abnormal physiological processes.
These abnormal physiological processes could be caused by genetic, neurochemical or neuroanatomical factors.
There are two key biological explanations for OCD:
1) Genetic explanation:
This includes the role of the COMT gene and the SERT gene (both of which are thought to affect levels of certain key neurotransmitters if they exist in a mutated form), as well as the idea that OCD is an inherited condition.
2) Neural explanations:
This includes abnormal levels of neurotransmitters such as dopamine and serotonin AND abnormal brain circuits (the “worry circuit”).
1) The Genetic Explanation for OCD
It may be the case that an individual inherits a specific gene from their parents that causes the onset of OCD.
This gene may then have an effect on levels of neurotransmitters in the brain, resulting in abnormal levels and the onset of the disorder.
Research has found that a person with a family member diagnosed with OCD is around 4x more likely to develop it as someone without.
The COMT Gene
The COMT gene is related to the production of a chemical called COMT, which is involved in the regulation of the neurotransmitter dopamine.
All genes come in different forms. This particular form of the COMT gene (a gene which we all have) has shown lower levels of activity, resulting in higher levels of dopamine (as it is not as heavily regulated).
The SERT Gene
This gene affects the transportation of serotonin - it may be that those with a mutated variation of this gene have lower levels of serotonin.
Why do some people possess variations of these genes (COMT/SERT) yet never develop OCD, whilst others do?
It may be the case that there is an interaction between GENES and the ENVIRONMENT…..
The gene may provide a genetic predisposition (vulnerability) to developing OCD;
And this is triggered by another factor, perhaps from the environment (biological or psychological) e.g. a stressor.
Grootheest et al. (2005)
procedure
Grootheest et al. conducted a meta-analysis, assessing 70 years of twin studies (10,034 twin pairs across 28 studies in total) into OCD, where MZ (identical – share 100% of their genes) twins are compared against DZ (non-identical – share 50% of their genes) twins.
A meta-analysis involves combining the results from many different studies (in this case OCD studies on twins).
Grootheest et al. (2005)
findings
In children, it was found that OCD symptoms are heritable, with genetic influences ranging from 45-65%.
In adults, it was found that OCD symptoms are heritable, with genetic influences ranging from 27-47%.
Grootheest et al. (2005)
conclusions
These findings suggest that twin studies indicate a genetic component to the transmission of OCD.
Heritability of OCD appears to be greater in children than adults.
Further support for the genetic explanation of OCD:
Nestadt et al. (2010) conducted a review of previous twin studies examining OCD. They found that 68% of identical twins (MZ) shared OCD as opposed to 31% of non-identical (DZ) twins, which suggests a very strong genetic component to OCD.
However, the fact that the concordance rate is not 100% suggests that environmental factors play a part too.
2) Neural Explanations
These genetic factors may lead to abnormalities in terms of the wiring of the brain and levels of certain key neurotransmitters (chemical messengers in the brain), resulting in OCD.
there are two key neurotransmitters that are implicated in OCD:
- Serotonin
- Dopamine
Where do obsessive thoughts originate from in the brain?
PET scans have shown that OCD sufferers can have relatively high levels of activity in the orbital frontal cortex (OFC).
The OFC is associated with higher level thought processes and the conversion of sensory information into thoughts.
This brain area is thought to help initiate activity upon receiving impulses to act, and then stop the activity when the impulse lessens.
Abnormal Brain Circuits
The caudate nucleus (located in the basal ganglia) normally suppresses worry signals from the orbital frontal cortex (OFC).
In turn, the OFC send signals to the thalamus about things that are worrying, such as a potential germ hazard.
When the caudate nucleus is damaged, it fails to suppress minor ‘worry signals’ (from the OFC) and the thalamus is alerted, which in turn sends signals back to the OFC, acting as a ‘worry circuit’ in the brain.
P: Evidence for neural explanations of OCD comes from Saxena and Rauch (2000).
E: They reviewed studies of OCD that used PET, fMRI and MRI neuro-imaging techniques to find consistent evidence of an association between the orbital frontal cortex and OCD symptoms.
C: This suggests that specific areas and mechanisms of the brain (specifically the OFC) are involved in the disorder.
