Biological Approach to Explaining OCD

• Genetic Explanations


  research suggests there's a strong genetic component to OCD

  explanation -> genetic predisposition to OCD passed on from one generation to another.

  Nestadt et al found 1st degree relatives of OCD sufferers had an 11.7% chance of developing the disorder, compared to a 2.7% in 1st degree relatives of control ppts. (known as a concordance rate
• Genetic Explanations


  'candidate genes' - genes identified as potentially causing a particular disease/illness due to previous knowledge

  response of OCD patients to certain drug therapies have led to suggestion these genes relating to serotonin and dopamine involved.

  COMT gene produces enzyme COMT helps regulate dopamine regulation.

  variation of this gene results in less COMT and more dopamine

  genes involving transmission of serotonin across synapses have been implicated in OCD e.g. 5HT1-D beta

  OCD may be aetiologically heterogenous -> means different types of OCD may have different genes/causes

  likely OCD is polygenic so there's several genes involved in this condition

  Taylor - study showed up to 230 genes may be involved in developing OCD
• Neural Mechanisms


  dopamine levels may be abnormally high in people with OCD - giving animals drugs which enhance dopamine lead to stereotyped repetitive movements like compulsions (Szechtman et al)

  serotonin is thought to play an important role in OCD and sufferers are thought to have lower levels than normal

  based on treatment evidence - giving OCD sufferers antidepressants reduce OCD symptoms
• Neural Mechanisms


  shown OCD sufferers have abnormalities in the functioning of their brain.

  e.g. thought there's an abnormality in a circuit in the brain involving the orbitofrontal cortex (OFC), caudate nucleus, thalamus and back to OFC.

  surgery in this circuit e.g. a lesion, leads to an improvement in symptoms in patients unresponsive to other treatments.

  thought the OFC notices when things are wrong and sends 'worry' signals.

  in OCD sufferers it's suggested the caudate nucleus is faulty so does NOT suppress signals and carries the message onto the thalamus which allows it to become a worry circuit
• frontal lobes


  involved in logically thinking
• parahippocampal gyrus


  evidence that the left parahippocampal gyrus functions abnormally in patients with OCD (responsible for processing unpleasant emotions)
• diathesis stress


  idea you will only develop a certain disorder (OCD) if you have a genetic vulnerability (diathesis) which is triggered by an environmental stressor (stress)

  genes or the environmental aren't enough by themselves
• Strength - role of genetics

  a meta-analysis of twin studies shows the likelihood that both monozygotic twins had OCD was 68% whereas this chance reduced to only 31% of dizygotic twins.

  MZ concordance rate is higher, and MZ twins share identical genes, this finding suggests that OCD is genetic
• Strength - research support for neural mechanisms

  there's research evidence supporting the role of neural mechanisms in causing OCD.

  since drug therapies that raise serotonin levels decrease OCD symptoms, this suggests that it was the lower levels of serotonin that caused the symptoms.

  therefore implies the idea that OCD is caused by abnormal serotonin functioning is valid
• Weakness - concordance rates aren't 100%

  concordance rates for MZ twins are not 100%. since these twins have identical genetic material, if one twin has OCD and it's purely genetic, then you would expect the other twin to also have it.

  consequently, OCD can't be solely due to genetics and there must be other explanations
• Weakness - genetic explanations isn't sufficient alone

  a more holistic explanation would be the diathesis-stress model. this is the idea a person has a vulnerability to OCD but the illness has to be triggered by an environmental stressor. this is a better explanation as it can account for why one MZ twins would have OCD but their identical twin didn't, and would also support the evidence that many OCD sufferers experience a traumatic event prior to developing OCD.

  so, the genetic explanation on its own isn't sufficient and the diathesis stress model is superior in explaining OCD
• Weakness - neural mechanisms may be flawed

  the idea that neural mechanisms causes OCD may be flawed as research is correlational.

  OCD patients have their neurochemical/brain structure analysed once they have developed OCD.

  so, abnormal functioning of neurochemistry and brain structure could be the effect of the OCD, not its cause.

  this reduces the validity of this biological explanation of OCD