The biological approach to explaining OCD

What two explanations are there to explaining OCD?

Genetic and Neural explanations

What is the genetic explanation?

Genes are involved in individual vulnerability to OCD.

Genes make up chromosomes and consist of DNA which codes the physical and psychological features of someone. Genes are transmitted from parents to offspring.

Aubrey Lewis observed that of his OCD patients, 37% had parents with OCD and 21% had siblings with OCD. This suggests that OCD runs in families and genetic vulnerability is passed down from one gen to the next.

What is the diathesis stress model? (Genetic explanation)

Certain genes leave some people more likely to develop a mental disorder but it is not certain.

Some environmental stress is necessary to trigger the condition (e.g. experience such as bereavement)

What is meant by candidate genes?(Genetic explanation)

Researchers have identified genes which create vulnerability for OCD (candidate genes):

1. COMT gene- This gene is involved in the production of the enzyme Catchecol - O - MethylTransferase

   This enzyme regulates neurotransmitter dopamine in the brain. This gene causes low levels of enzyme which means high levels of dopamine = OCD

2. SERT gene - This creates a protein which removes serotonin and recycles it. If the gene creates too much of the protein, serotonin levels decrease. Low serotonin levels = OCD

What is meant by ‘OCD is polygenic’? (Genetic explanation)

OCD is not caused by one single gene but by a combination of genetic variations that together significantly increase vulnerability.

Steven Taylor found evidence that up to 230 different genes may be involved in OCD.

What is the neural explanation?

The view that OCD is determined by the behaviour of the nervous system, in particular the brain and individual neurons.

What is the role of serotonin? (Neural explanation)

The neurotransmitter serotonin regulates mood.

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

If a person has low levels of serotonin then normal transmission of mood-relevant info does not take place and a person may experience low moods.

What is the basal ganglia? (Neural explanation)

Basal ganglia

Hypersensitivity gives a rise to the repetitive motor behaviours seen in OCD e.g. repetitive washing, cleaning or checking

What is the left parahippocampal gyrus? (Neural explanation)

OCD is associated with impaired decision making. This may be associated with abnormal functioning of the lateral areas of the frontal lobes of the brain.

The frontal lobes are responsible for logical thinking and making decisions.

The left parahippocampal gyrus is associated with processing unpleasant emotions, functions abnormally in OCD.

What is a strength of the genetic explanations of OCD?

Strong evidence base

Evidence to suggest that some people are vulnerable to OCD as a result of their genetic makeup.

Gerald Nestadt et al reviewed twin studies and found that 68% of identical twins shared OCD as opposed to 31% of non-identical twins.

Marini and Stebnicki found that a person with a family member diagnosed with OCD is around 4 times more likely to develop it as someone without.

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

What is a limitation of the genetic explanations of OCD?

Environmental risk factors

OCD does not appear to be entirely genetic in origin and environmental risk factors can also trigger or increase the risk of developing OCD.

Cromer et al 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.

What is a strength of the neural explanations of OCD?

Supporting evidence

Antidepressants that work purely on serotonin are effective in reducing OCD symptoms and this suggests that serotonin may be involved in OCD.

Also, OCD symptoms form part of conditions that are known to be biological in origin (e.g. Parkinsons which causes muscle tremors and paralysis). If a biological disorder produces OCD symptoms then we may assume the biological processes underlie OCD.

This suggests that biological factors may be responsible for OCD.

What is a limitation of the neural explanations of OCD?

Serotonin - OCD link may not be unique to OCD

Many people with OCD also experience clinical depression. Having 2 disorders together is called co-morbidity. This depression involves disruption to the action of serotonin.

This leaves us with a logical problem when it comes to serotonin as a possible basis for OCD. It could be that serotonin activity is disrupted in many people with OCD because they are depressed as well.

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