Biological explanation for OCD

• A candidate gene is a gene that is associated with or suspected of causing a particular disorder/disease
• One possible gene linked with OCD is the SERT gene
• The serotonin transporter (SERT) is responsible for removing excess serotonin from synapses, so if there's an abnormality here it could lead to too much serotonin being left behind which may cause symptoms of OCD
• Studies have found that people with OCD are more likely than controls to carry a variant of the SERT gene called LPR allele

  However, this finding has not been consistent across all studies - some have failed to find any association between the LPR allele and OCD
• Concordance rates means percentage of pairs where both individuals share specific characteristics in a sample of pairs of identical and non identical twins
• MZ = monozygotic twins (identical)
• DZ = dizygotic twins (non-identical)
• If monozygotic twins have a higher concordance rate than dizygotic twins then it suggests a genetic factor as the identical twins share more genes. if monozygotic twins have a lower concordance rate than dizygotic twins, then it suggests environmental factors
• What was Cromer's study into OCD?

  Found that over half the OCD patients they studied experiences a traumatic event in their lifetime. Therefore OCD may be explained by diathesis stress
• Diathesis Stress Model is when an individual has a predisposition or vulnerability to develop a disorder but only does so under certain conditions such as experiencing trauma.
• OCD sufferers have a high level of activity in their orbito-frontal cortex
• The orbito-frontal cortex is involved in decision making , impulse control and logical thinking
• The neural explanation for OCD is : low or abnormal levels of neurotransmitters like serotonin and dopamine are present. People with OCD have a higher level of activity in their orbito-frontal cortex.
• Serotonin is associated with mood regulation and anxiety
• Dopamine is associated with pleasure and reward
• How do low levels of neurotransmitters like serotonin produce OCD?

  Lower levels of serotonin means less available to inhibit post synaptic neuron firing, therefore more signals may fire than normal
• Low levels of serotonin can lead to an increase in the number of false alarms sent by the brain which leads to excessive checking behaviour
• High levels of dopamine can cause obsessive thoughts as it increases the likelihood that certain stimuli will be perceived as important
• Give two limitations of neural explanations for OCD

  LIMITATIONS:

  •  there is no evidence to support the idea that people with OCD actually have lower levels of serotonin compared to non-sufferers
  • the co-morbidity of OCD and depression, cannot be sure if serotonin level is disrupted due to OCD or whether serotonin levels are different due to the depression they experience