Explaining OCD:

• What are the two different biological explanations for OCD?

  1. Genetic explanations
  2. Neural explanations
• What is the genetic explanation?

  Genes make up chromosomes and consist of DNA which codes the physical features of an organism (such as eye colour, height) and psychological features (such as mental disorder, intelligence). Genes are transmitted from parents to offspring. i.e. inherited
• What is the neural explanation?

  The view that physical and psychological characteristics are determined by the behaviour of the nervous system, in particular the brain as well as individual neurons.
• What are the three different parts to the genetic explanation?

  1. Candidate genes
  2. OCD is polygenic
  3. Different types of OCD
• Candidate genes:

  Researchers have identified specific genes which create a vulnerability for OCD, called candidate genes.

  • Serotonin genes, are implicated in the transmission of serotonin across synapses
  • Dopamine genes are also implicated in OCD and may regulate mood.

  Both serotonin and dopamine are neurotransmitters.
• OCD is polygeneic:

  • OCD is not caused by one single gene but several genes are involved
  • Taylor (2013) found evidence that up to 230 different genes may be involved in OCD
• Different types of OCD:

  • One group of genes may cause OCD in one person but a different group of genes may cause the disorder in a different person- known as aetiologically heterogeneous
  • There is also evidence that different types of OCD may be the result of particular genetic variations, such as hoarding disorder and religious obsession
• What are the three different parts of the neural explanation?

  1. Low levels of serotonin lowers mood
  2. Decision making systems in frontal lobes impaired
  3. Parahippocampul gyrus dysfunctional
• Low levels of serotonin lowers mood:

  • Neurotransmitters are responsible for relaying information from one neuron to another
  • For example if a person has low levels of serotonin then normal transmission of mood-relevant information does not take place and mood (and sometimes other mental processes) is affected
• Decision-making systems in frontal lobes impaired:

  • Some cases of OCD, and in particular hoarding disorder, seem to be associated with impaired decision making
  • This in turn may be associated with abnormal functioning of the lateral (side bits) frontal lobes of the brain
  • The frontal lobes are responsible for logical thinking and making decisions
• Parahippocampal gyrus dysfuntioncal:

  There is also evidence to suggest that an area called the left parahippocampal gyrus, associated with processing unpleasant emotions, functions abnormally in OCD.
• Strength of the genetic explanation:

  Nestadt et al (2010) reviewed twin studies and found that 68% of identical twins (MZ) shared OCD as opposed to 31% of non-identical (DZ) twins.

  This suggests that there is a genetic basis for OCD. This study shows that the closer you are in genetic relatedness to someone with OCD, the more likely you are to suffer from the disorder.
• Limitation of the genetic explanation:

  P- Genetic variation affects vulnerability to OCD, but there are also environmental risk factors that trigger or increase the risk of OCD.

  E- Cromer et al (2007) found in one sample over half of people with OCD experienced a traumatic event. OCD severity correlated positively with a number of traumas.

  L- This means that genetic vulnerability only provides a partial explanation for OCD
• Strength of the neural model:

  Antidepressants that work purely on serotonin (increase levels of serotonin) are effective in reducing OCD symptoms. In a review of 17 studies, symptoms reduced for around 70% of people taking SSRIs (soomro et al 2009)

  This is evidence that an imbalance of neurotransmitters may cause OCD.

  If medication helps to reduce the symptoms of OCD by balancing out the level of serotonin, it must be a cause in the first place.
• Limitation of the neural model:

  The medication is not effective for everyone which suggests that it's not a cause for everyone

  Low serotonin have also been involved in other disorders, such as depression
• Strength of the genetic explanation:

  Nestadt et al (2000) identified 80 patients with OCD and 343 of their first-degree relatives and compared them with 73 control patients without mental illness and 300 of their relatives. They found that people with a first degree relative with OCD had a five times greater risk of having OCD themselves at some time in their lives, compared to the general population.

  This shows that there must be a genetic link in the development of OCD.

  This provided evidence that OCD runs in families. If you share 50% of your genes with someone you are more likely to suffer from the disorder.
• Strength of the neural explanation:

  Frontal lobes are the front part of the brain that are responsible for logical thinking and making decisions. There is evidence in OCD sufferers of abnormal functioning of the lateral bits of the frontal lobes. There is also evidence to suggest that an area known as the parahippocampal gyrus, associated with processing unpleasant emotions, functions abnormally in OCD.

  This shows that certain brain structures may be involved in OCD.

  Abnormal functioning of certain brain parts which may be associated with impaired decision making may be causing the irrational thoughts which are a symptom of OCD.